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Proceedings ArticleDOI

Performance of Cognitive Hybrid Automatic Repeat reQuest: Stop-and-Wait

11 May 2015-pp 1-5
TL;DR: This paper analyzes both the throughput and delay performance of the CSW-HARQ system, for which a range of closed-form formulas are derived that are also validated by simulation results.
Abstract: Detecting spectrum holes and efficiently accessing them are the two basic functions that enable a cognitive radio (CR) to make use of the licensed spectrums of a primary radio (PR). In this paper, we consider a CR scheme, which opportunistically accesses a PR channel for communication between a pair of nodes based on the stop-and-wait hybrid automatic repeat request (SW-HARQ). Hence, it is referred to as the cognitive SW-HARQ (CSW-HARQ) arrangement. In our CSW-HARQ system, the PR channel is modelled as a two-state Markov chain having `On' and `Off' states. The CR may only access the PR channel in its `Off' state. In this paper, we analyze both the throughput and delay performance of the CSW-HARQ system, for which a range of closed-form formulas are derived that are also validated by simulation results. Our performance results show that both the activities of PR users and the reliability of the CR channel have a substantial impact on the achievable performance of the CR system.

Summary (3 min read)

Introduction

  • Recent studies conducted both by the Federal Communication Commission (FCC) in the USA and by the European Telecommunications Standards Institute (ETSI) in Europe reveal that under the conventional static spectrum allocation policy substantial segments of the earmarked electromagnetic spectrum are heavily under-utilized [1]–[4].
  • Corresponding to this scenario, a timeslot (TS) of duration T is divided in the sensing epoch (Ts) and the transmission epoch (Td).
  • The principle of their CSW-HARQ scheme is outlined in Section II-B. Section III analyses the attainable throughput and delay performance, followed by the performance results given in Section IV.

A. PR System and Assumptions

  • The authors assume that the PR system uses the channel according to a discrete-time Markov chain having two states, namely ‘On’ and ‘Off’, as shown in Fig.
  • The transition probabilities from the ‘On/Off’ state to the ‘Off/On’ state are expressed as α and β, respectively.
  • Let us assume that the probabilities of the PR system being in the ‘On’ and ‘Off’ states are Pon and Poff = 1 − Pon, which are the probability of the channel being occupied by the PR and that of the channel being free from the PR.
  • Then, provided that the Markov chain is in its steady state, the authors have [16].
  • For simplicity, the authors assume that the activities of the PR users within different TSs are independent of each other.

B. Cognitive Stop-and-Wait Hybrid Automatic Repeat Request

  • The authors assume that the CR system works in the high SNR region of the PR system, and it is capable of reliably sensing the ‘On/Off’ state of the PR channel, without false-alarm and also without miss-detection.
  • Otherwise, the CR transmitter waits and senses again the PR channel at the commencement of the next time-slot.

C. Operation of the CR Transmitter

  • In the classic SW-HARQ, the transmitter sends a single packet in a TS and then waits for its feedback, which is expected to be received within a specified round-trip time (RTT).
  • Otherwise, it has to wait and sense again.
  • 8: if the ith packet is received error-free then 9: receiver sends ACK signal.
  • Similar to the principle of the classic SW-HARQ schemes [16]– [19], in their proposed CSW-HARQ arrangement, the CR transmitter is not allowed to transmit or retransmit its packets, while it is waiting for the feedback flag of the transmitted packet.
  • Hence, if a positive feedback (i.e., ACK) of a packet is received by the original transmitter node within the RTT, then this packet is deleted from the transmitter buffer and a new packet is transmitted in the next free TS.

D. Operation of the CR Receiver

  • When the CR receiver receives a packet from the CR transmitter, it invokes RS error-correction/detection and then generates a feedback flag accordingly.
  • The authors assume that the feedback channel is perfect, and the receiver has a buffer of size one, which is updated only when a packet is correctly received [16]–[18].
  • Therefore, an ACK signal is fed back for this packet and the sequence index of the receiver buffer is increased by one.
  • After receiving the feedback of the corresponding packet, the CR transmitter senses the next free TS and transmits a new packet, i.e. packet 2, as seen in Fig.
  • The above process continues, until all packets are successfully received by the CR receiver.

III. PERFORMANCE ANALYSIS OF CSW-HARQ

  • The authors analyze both the attainable throughput and the average packet delay.
  • In their analysis of the average packet delay, the total time spanning from the start of the PR channel’s sensing to the successful transmission of all the packets is taken into account, i.e. both the free and busy TSs are counted right from the start of the CR system’s activation for transmission of a block of packets.
  • In their analysis, the authors assume that the time required for preparing packets and the ACK/NACK feedback duration can be ignored.
  • Furthermore, the authors assume that the errors generated by the undetectable errors of the RS code can be ignored.

A. Delay

  • In contrast to the classic SW-HARQ, where the delay is only imposed by the channel introduced errors, in their CSW-HARQ, the delay includes both that caused by channel errors and by the lack of free channels for the CR transmitter to use.
  • Let TDP and TD represent the delay imposed by the PR channel’s busy state and the delay incurred by the CR to successfully transmit a packet to the CR receiver, respectively.

B. End-to-End Throughput

  • The throughput of their CSW-HARQ scheme can be defined as the total number of packets successfully delivered from the CR transmitter to the CR receiver per TS.
  • Explicitly, the event of successfully delivering a packet depends on two events: (a) the CR transmitter successfully detects a free TS and (b) the CR transmitter uses the free TS to successfully deliver a packet.
  • This implies that the packet is only successfully delivered within the ith TS.
  • Therefore, the probability PS(i) can be expressed as PS(i) = i∑ j=1 Poff (j|i)PS(j|i), (7) where Poff (j|i) denotes the probability that the PR channel is free in j out of the i TSs, while PS(j|i) denotes the probability that the CR transmitter uses j.

IV. PERFORMANCE RESULTS

  • Fig. 5 depicts the throughput of the CSW-HARQ scheme versus the packet error probability (PF ) for various PR channel occupancy probabilities of Pon.
  • Additionally, the authors can see that the analytical results evaluated from Equation (9) agree well with the simulation results.
  • The average delay also increases, when the channel occupancy of the PR users increases.
  • When making a close comparison between Fig. 6 and Fig. 8, the authors find that the average end-to-end packet delay is lower than the corresponding average packet delay.

V. CONCLUSIONS

  • Both the throughput and delay performance of the proposed CSW-HARQ scheme have been investigated both by analysis and simulations.
  • A range of formulas have been derived and the performance of the CSW-HARQ systems has been compared from different perspectives.
  • The authors simulation results demonstrates that the analytical formulas are accurate.
  • When the PR channel is busy, the CSW-HARQ’s throughput might become very low and its packet delay might become excessive, even when the CR’s communication channel is reliable.

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Performance of Cognitive Hybrid Automatic Repeat reQuest:
Stop-and-Wait
Ateeq Ur Rehman, Lie-Liang Yang, and Lajos Hanzo
School of Electronics and Computer Science, University of Southampton, SO17 1BJ, UK.
(E-mail: aur1g12, lly, lh@ecs.soton.ac.uk, http://www-mobile.ecs.soton.ac.uk)
Abstract—Detecting spectrum holes and efficiently accessing them are
the two basic functions that enable a cognitive radio (CR) to make use
of the licensed spectrums of a primary radio (PR). In this paper, we
consider a CR scheme, which opportunistically accesses a PR channel
for communication between a pair of nodes based on the stop-and-wait
hybrid automatic repeat request (SW-HARQ). Hence, it is referred to as
the cognitive SW-HARQ (CSW-HARQ) arrangement. In our CSW-HARQ
system, the PR channel is modelled as a two-state Markov chain having
‘On’ and ‘Off states. The CR may only access the PR channel in its ‘Off
state. In this paper, we analyze both the throughput and delay performance
of the CSW-HARQ system, for which a range of closed-form formulas are
derived that are also validated by simulation results. Our performance
results show that both the activities of PR users and the reliability of the
CR channel have a substantial impact on the achievable performance of
the CR system.
I. INTRODUCTION
Recent studies conducted both by the Federal Communication Com-
mission (FCC) in the USA and by the European Telecommunications
Standards Institute (ETSI) in Europe reveal that under the conventional
static spectrum allocation policy substantial segments of the earmarked
electromagnetic spectrum are heavily under-utilized [1]–[4]. As a
result, the earmarked bandwidth cannot be exploited, whilst the readily
available spectrum remains insufficient for innovative new wireless
applications [3], [5]. This inefficient spectrum exploitation motivates
the concept of dynamic spectrum access, which allows cognitive radio
users (CRUs) to access and utilize the unoccupied spectrum holes,
which have traditionally been exclusively assigned to primary radio
users (PRUs) [5], [6].
The concept of CR was introduced by Mitola [7], which emerged
as a promising paradigm for addressing the problem of spectrum
scarcity. A CR is capable of detecting the unoccupied portions of
the licensed spectrum and of efficiently accessing them for its own
data transmission without affecting the legal rights of PRUs [8], [9].
Moreover, the CR is required to vacate the licensed spectrum as soon
as the PRUs wish to access them. In order to improve the exploitation
of the licensed spectrum, the regulatory bodies officially allow CRs to
access and to opportunistically exploit the PR spectrum. As a result,
the first CR based standard, namely IEEE 802.22, was ratified for
wireless regional area networks (WRAN) [10].
In this paper, we propose a cognitive stop-and-wait hybrid automatic
repeat request (CSW-HARQ) scheme. We focus our attention on
opportunistic spectrum access in CR systems, where a CRU senses and
occupies a PR channel for its own transmission, provided that the PR
channel is free from PRUs. In order to analyze and detect the activity
of PRUs on a channel, a number of sensing techniques were proposed
in the literature [5], [11]–[14]. Specifically, in our studies, the activity
of a PR channel is modelled using a two-state Markov chain [15], with
the two states representing the ‘On’ and ‘Off status of PRUs. If the
PR channel is deemed to be in its ‘Off state, the CR accesses the
channel for its own transmission. Otherwise, it waits until the next
time-slot and senses again. Corresponding to this scenario, a time-
slot (TS) of duration T is divided in the sensing epoch (T
s
) and the
transmission epoch (T
d
). The sensing epoch T
s
is used for detecting
spectrum holes, while the transmission epoch T
d
= T T
s
is used for
data transmission. In our CR system, the data transmission relies on
the principles of classic stop-and-wait hybrid automatic repeat request
(SW-HARQ) [16]–[18].
Automatic Repeat reQuest (ARQ) constitutes an efficient technique
of reliable data transmission over noisy channels. The concept of
ARQ was originally introduced by Chang [19], which was then clas-
sified into three popular ARQ protocols: Stop-and-Wait ARQ (SW-
ARQ), Go-Back-N ARQ (GBN-ARQ) and Selective-repeat ARQ (SR-
ARQ) [16]–[18]. The principle of ARQ is appealingly simple. After
transmitting a packet, if the original transmitter node fails to receive
a positive acknowledgement within the defined time duration or if
it receives a negative acknowledgement, the packet is retransmitted.
The ARQ protocols are capable of achieving reliable data transmis-
sion, provided that the channel-induced error rate remains moderate.
However, beyond a certain error rate both the throughput and the delay
may become inadequate. Hence, for the sake of enhancing the per-
formance, hybrid Forward Error Correction (FEC) and ARQ (HARQ)
schemes [20], [21] may be employed. In addition to detecting errors, in
HARQ, the FEC scheme also has the capability of correcting a number
of errors and the ARQ mechanism is activated for the retransmission
of a packet, when residual errors are detected after FEC decoding. As
a benefit, HARQ schemes are typically capable of providing a better
throughput/delay performance than the corresponding ARQ schemes.
Hence, they have been widely used in wireless communication sys-
tems [22], [23].
In this paper, our proposed CSW-HARQ scheme intrinsically amal-
gamates CR with the classic SW-HARQ regime. It first senses a PR
channel and, if finds it free, it accesses the channel and transmits
packets using our CSW-HARQ scheme. In this paper, Reed-Solomon
(RS) codes are used for error correction and detection [24]–[26].
We investigate both by analysis and simulations both the achievable
throughput and delay performance of CSW-HARQ. We will demon-
strate that both the behaviour of the PR users as well as the quality of
the CR channel have a substantial impact on the achievable throughput
and delay performance of the CR system.
The rest of this paper is organized as follows. The system considered
is described in Section II. The principle of our CSW-HARQ scheme is
outlined in Section II-B. Section III analyses the attainable throughput
and delay performance, followed by the performance results given in
Section IV. Finally, our conclusions are presented in Section V.
II. S
YSTEM MODEL
A. PR System and Assumptions
Let us consider a communication channel, which allows a PR
system to transmit packets of duration T
p
. We assume that the PR
system uses the channel according to a discrete-time Markov chain
having two states, namely ‘On’ and ‘Off’, as shown in Fig. 1. The
transition probabilities from the ‘On/Off state to the ‘Off/On’ state are
expressed as α and β, respectively. Let us assume that the probabilities
of the PR system being in the ‘On’ and ‘Off states are P
on
and
P
of f
=1 P
on
, which are the probability of the channel being
occupied by the PR and that of the channel being free from the PR.
978-1-4799-8088-8/15/$31.00 ©2015 IEEE

State
(ON)
State
(OFF)
1-α
α
β
1-β
β
α+β
α
α+β
Fig. 1. Two-state discrete-time Markov chain model of the PR system.
Then, provided that the Markov chain is in its steady state, we have
[16]
P
on
α = P
of f
β, (1)
which gives
P
on
=
β
α + β
,P
of f
=
α
α + β
. (2)
Channel
Off Off
On
T
TT
t
(a) Pattern of channel usage by a PR
Transmission
Sensing
Transmission
Sensing
Transmission
Sensing
Channel
T
T
s
T
T
d
= T T
s
T
s
T
T
d
= T T
s
T
s
No-
t
(b) Pattern of channel usage by a CR
Fig. 2. Time-slot structure of a CR system having a sensing duration T
s
and a
transmission duration T
d
, when the total duration of a time-slot is T [27].
We assume that in the PR system the time is divided into TSs of
duration T and that the PR users always activate the channel at the start
of a TS, as shown in Fig. 2(a). When the channel is ‘On’, one of the PR
users occupies the channel and transmits a few packets. By contrast, if
the channel is detected to be in the ‘Off state, a CR user accesses the
channel and transmits its packets. For simplicity, we assume that the
activities of the PR users within different TSs are independent of each
other.
B. Cognitive Stop-and-Wait Hybrid Automatic Repeat Request
We assume that the CR system works in the high SNR region of the
PR system, and it is capable of reliably sensing the ‘On/Off state of
the PR channel, without false-alarm and also without miss-detection.
The time-slots in the CR system are structured in a form as shown Fig.
2(b). Within a time-slot of T seconds, the CR transmitter dedicates T
s
seconds at the start to channel sensing and then uses the remaining
T
d
= T T
s
seconds to transmit data, provided that the PR channel is
found in the ‘Off state. Otherwise, the CR transmitter waits and senses
again the PR channel at the commencement of the next time-slot. In
the CR system, the data to be transmitted are assumed to be encoded
by a RS code RS(N
d
,K
d
) [17], where K
d
and N
d
represent the
number of information and coded symbols, respectively. We assume
for simplicity that a CR packet is encoded by a single RS codeword,
which is transmitted during T
p
<T
d
seconds. We assume that the RS
code is capable of correcting t =(N
d
+ K
d
)/2 symbol errors and
that it has a perfectly reliable error-detection probability of one, as and
when there are uncorrectable errors.
Given the above assumptions, the data are transmitted between a
pair of CR users over the PR channel based on the principles of our
CSW-HARQ scheme, which is characterized in Fig. 3 as well as in
Algorithm 1 and detailed below.
CR Transmitter
CR Receiver
Is PR channel
Y(o)
free?
Transmitting
apacket
sensing
correct?
Is the packet
N (NACK)Y(ACK)
PR channel
Wireless channel
N
(on)
Fig. 3. Flow chart showing the operations of the proposed CSW-HARQ
scheme.
Transmission
1
2
1
2
3
23
Off
Busy
Channel
2
e
No−
transmission
On
Off
Off
Off
ACK
ACK
N
A
C
K
ACK
CR-receiver
T
s
T
s
T
s
T
s
T
p
CR-transmitter
T
s
T
p
T
p
T
p
T
w
T
w
T
w
T
w
T
T
d
=T -T
s
T
d
T
T
d
Fig. 4. The transmission flow of the proposed CSW-HARQ scheme. The total
duration of each time-slot is T = T
s
+ T
d
,whereT
d
consists of a packet’s
transmission duration and its waiting epoch T
w
.
C. Operation of the CR Transmitter
In the classic SW-HARQ, the transmitter sends a single packet in a
TS and then waits for its feedback, which is expected to be received
within a specified round-trip time (RTT). By contrast, in the CSW-
HARQ, the CR transmitter has to sense the PR channel before the
transmission or retransmission of a packet. If the PR channel is deemed
to be in the ‘Off state, the CR transmitter sends a packet. Otherwise,
it has to wait and sense again. Again, the CSW-HARQ procedure is
portrayed in both the Algorithm 1 as well as in Fig. 3. Similar to the
classic SW-HARQ scheme, the CR transmitter has a buffer of size one,
which is updated based on the feedback flag of each packet.
We assume that all packets are of the same length and that the CR
Algorithm 1 : CSW-HARQ Algorithm
1: Initialization: M
c
= number of packets, T
d
= N , T
s
= k, i =1,
TS=1.
2: Input: T
d
, T
s
, packets.
3: while i M
c
do
4: CR transmitter senses a time-slot (TS).
5: if TS is free then
6: transmits the ith packet and, then,
7: waits for T
w
duration to receive feedback.
8: if the ith packet is received error-free then
9: receiver sends ACK signal.
10: i = i +1.
11: else
12: receiver sends NACK.
13: end if
14: else
15: waits until the next TS.
16: end if
17: TS=TS+1.
18: end while

transmitter is always ready to transmit these packets in free TSs. As
shown in Fig. 4, each CR packet consists of a RS coded codeword,
which is transmitted within the duration of T
p
seconds. After transmis-
sion of a packet, the CR transmitter waits for T
w
duration in order to
receive its feedback. We assume that the RTT is T
d
, which is the time
interval between the transmission of a packet and the instant, when
its feedback is received. Therefore, in our CSW-HARQ scheme, the
feedback of each packet is received within the RTT of duration T
d
,as
showninFig.4.
Similar to the principle of the classic SW-HARQ schemes [16]–
[19], in our proposed CSW-HARQ arrangement, the CR transmitter
is not allowed to transmit or retransmit its packets, while it is waiting
for the feedback flag of the transmitted packet. Hence, if a positive
feedback (i.e., ACK) of a packet is received by the original transmitter
node within the RTT, then this packet is deleted from the transmitter
buffer and a new packet is transmitted in the next free TS. However,
if a negative feedback (i.e., NACK) is received, then the transmitter
retransmits the erroneous packet in the next free TS.
D. Operation of the CR Receiver
When the CR receiver receives a packet from the CR transmitter, it
invokes RS error-correction/detection and then generates a feedback
flag accordingly. Specifically, if a packet is correctly detected by
the RS decoder, an ACK signal is fed back to the CR transmitter,
otherwise, a NACK signal is sent to the CR transmitter for requesting
retransmission. In this paper, we assume that the feedback channel is
perfect, and the receiver has a buffer of size one, which is updated only
when a packet is correctly received [16]–[18].
For example, as shown in Fig. 4, packet 1 is correctly received by
the CR receiver. Therefore, an ACK signal is fed back for this packet
and the sequence index of the receiver buffer is increased by one. After
receiving the feedback of the corresponding packet, the CR transmitter
senses the next free TS and transmits a new packet, i.e. packet 2,as
seen in Fig. 4. However, this packet is seen to be detected in error after
RS decoding. Therefore, the CR receiver uses a NACK signal to ask the
CR transmitter for a retransmission. After the reception of the NACK
signal, the CR transmitter retransmits packet 2 in the next TS, since
the PR channel is detected to be free in this TS. By contrast, as shown
in Fig. 4, if the PR channel is found to be in the ‘On’ state (Busy), the
CR transmitter stops its transmissions and it waits until the next TS
and senses again. The above process continues, until all packets are
successfully received by the CR receiver.
III. P
ERFORMANCE ANALYSIS OF CSW-HARQ
In this section, we analyze both the attainable throughput and the
average packet delay. In our analysis of the average packet delay, the
total time spanning from the start of the PR channel’s sensing to the
successful transmission of all the packets is taken into account, i.e.
both the free and busy TSs are counted right from the start of the
CR system’s activation for transmission of a block of packets. By
contrast, in our simulations reported in Section IV, we additionally
consider another type of delay, referred to as the end-to-end packet
delay, which is the time from the start of transmitting a packet to the
instant that the packet is confirmed to be successfully received. In our
analysis, we assume that the time required for preparing packets and
the ACK/NACK feedback duration can be ignored. Furthermore, we
assume that the errors generated by the undetectable errors of the RS
code can be ignored.
A. Delay
In contrast to the classic SW-HARQ, where the delay is only
imposed by the channel introduced errors, in our CSW-HARQ, the
delay includes both that caused by channel errors and by the lack
of free channels for the CR transmitter to use. Let T
DP
and T
D
represent the delay imposed by the PR channel’s busy state and the
delay incurred by the CR to successfully transmit a packet to the
CR receiver, respectively. Then, given the probability P
on
of the PR
system, where P
on
is defined in (2), the average delay T
DP
for the CR
system to find a free channel can be formulated as
T
DP
=E [T
DP
(i)]
=E [(i 1)T ]
=
i=1
(i 1)TP
i1
on
(1 P
on
)
=
P
on
T
1 P
on
(3)
where T
DP
(i) denotes the delay, when the CR transmitter detects that
the ith TS is free for its use, while the previous (i 1)TSsarebusy,
which gives a delay of (i1)T . Furthermore, when substituting P
on
=
β/(α + β) from (2) into the above equation, we arrive at
T
DP
=
βT
α
. (4)
The average packet delay T
D
can be expressed as
T
D
=E [T
D
(i)]
=E [(i(T
DP
+ T )] , (5)
where T
D
(i) denotes the average delay, when the CR transmitter
uses in total i transmissions to successfully send a packet to the CR
receiver. Explicitly, we have T
D
(i)=i(T
DP
+ T ), since for every
CR transmission, the CR transmitter requires in average duration of
T
DP
to find a free TS and then uses the free TS to transmit a packet.
Let us denote the packet error probability after RS decoding by P
F
.
Then, we have
T
D
=
i=1
i(T
DP
+ T )P
i1
F
(1 P
F
)
=
(α + β)T
α
i=1
iP
i1
F
(1 P
F
)
=
1+
β
α
T
1 P
F
(seconds). (6)
Eq.(6) shows that when the PR channel becomes busier, resulting in
an increase of β/α, and/or when the CR channel becomes less reliable
reflected by the increase of P
F
, the average packet delay increases.
B. End-to-End Throughput
The throughput of our CSW-HARQ scheme can be defined as the to-
tal number of packets successfully delivered from the CR transmitter to
the CR receiver per TS. Explicitly, the event of successfully delivering
a packet depends on two events: (a) the CR transmitter successfully
detects a free TS and (b) the CR transmitter uses the free TS to
successfully deliver a packet. Let us express the probability P
S
(i)
that a packet is successfully delivered by the CR transmitter to the CR
receiver using i TSs. This implies that the packet is only successfully
delivered within the ith TS. For the other (i 1) TSs, the PR channel
might be occupied by the PR user or the packet was received in error,
hence requires retransmission. Therefore, the probability P
S
(i) can be
expressed as
P
S
(i)=
i
j=1
P
of f
(j|i)P
S
(j|i), (7)
where P
of f
(j|i) denotes the probability that the PR channel is free in
j out of the i TSs, while P
S
(j|i) denotes the probability that the CR

transmitter uses j TSs to transmit the packet successfully to the CR
receiver. Hence, we have
P
S
(i)=
i
j=1
i
j
P
j
of f
P
ij
on
P
j1
F
(1 P
F
)
=
i
j=1
i
j
α
α + β
j
β
α + β
ij
P
j1
F
(1 P
F
). (8)
Based on the above analysis, the total number of packets success-
fully delivered by the CR transmitter to the CR receiver per TS, which
is the normalized throughput, can be expressed as
R
s
=
i=1
1
i
× P
S
(i)
=
i=1
i
j=1
1
i
i
j
α
α + β
j
β
α + β
ij
× P
j1
F
(1 P
F
)(packets per TS). (9)
Furthermore, if we express the throughput in terms of packets per
T
p
(packet duration), we have
R
s
=
T
p
T
× R
s
=
T
p
T
s
+ T
d
× R
s
(packets per T
p
). (10)
IV. P
ERFORMANCE RESULTS
In this section, both the throughput and delay performance of the
CSW- HARQ scheme are characterized in terms of two factors: 1)
the PR channel’s relative occupancy reflected by P
on
, and 2) the CR
channel’s reliability quantified by P
F
.
0.0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Normalized Throughput (Packet / T
p
)
0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Packet Error Probability (P
F
)
Theory
Sim
P
on
=0:0.1:0.8
Fig. 5. Throughput performance of our CSW-HARQ scheme versus the packet
error probability (P
F
) for various probabilities of the channel being busy
(P
on
), when we have T
s
=1T
p
and T
d
=2T
p
.
Fig. 5 depicts the throughput of the CSW-HARQ scheme versus the
packet error probability (P
F
) for various PR channel occupancy prob-
abilities of P
on
. In our simulations, the throughput (R
S
) is calculated
according to:
R
S
=
N
s
N
t
×
T
p
T
s
+ T
d
(packets per T
p
), (11)
where N
t
represents the total number of TSs used for the successful
transmission of N
s
packets by the CR. For a given P
on
, it is observed
from Fig. 5 that the throughput of CSW-HARQ is at its maximum,
when P
F
=0.However,anincreaseofP
F
degrades the reliability of
the channel, resulting in an increased number of retransmitted packets
and hence in a reduced throughput. Additionally, for a given P
F
,the
throughput of the CSW-HARQ scheme is maximum, when the PR
channel is always ‘Off’, corresponding to P
on
=0.However,when
the probability of the PR channel’s occupancy increases, i.e. if the
value of P
on
increases from 0 to 0.8, the throughput of the CR system
is reduced, since the CR system has less opportunities for transmission
over the PR channel. Additionally, we can see that the analytical results
evaluated from Equation (9) agree well with the simulation results.
0
5
10
15
20
25
30
Average Packet Delay Normalized by T
p
0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Packet Error Probability (P
F
)
Theory
Sim
P
on
=0:0.1:0.8
Fig. 6. Average packet delay of the CSW-HARQ system versus the packet
error probability, when we have T
s
=1T
p
and T
d
=2T
p
.
Fig. 6 portrays the average packet delay of the CSW-HARQ scheme.
In our simulations, the average packet delay (T
DS
) is obtained by:
T
DS
=
N
t
× (T
s
+ T
d
)
N
s
(seconds). (12)
Fig. 6 shows that the average packet delay of the CSW-HARQ scheme
is at its minimum, when the CR channel is error free, i.e. when
P
F
=0, and the probability of the PR channel occupancy is zero,
i.e. P
on
=0. The average delay increases with the degradation of
the CR channel. The average delay also increases, when the channel
occupancy of the PR users increases. Again, the comparison between
analytical and simulation results shown in Fig. 6 demonstrates that
Eq. (6) is accurate.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Probability
0 5 10 15 20 25 30 35
Number of time-slot (TS)
P
on
= 0.3
♣♣
P
F
= 0.1
P
F
= 0.3
P
F
= 0.5
0.0
0.0005
0.001
0.0015
0.002
0.0025
11 12 13 14 15
Zoom
0.0
0.00002
0.00004
0.00006
0.00008
0.0001
0.00012
0.00014
19 20 21 22 23
Zoom
Fig. 7. Probability of a specific end-to-end packet delay of the CSW-HARQ
system expressed as a function of the number of TSs for various values of P
F
,
P
on
=0.3, T
s
=1T
p
and T
d
=2T
p
.
The probability mass function (PMF) of the end-to-end packet delay
generated by the CSW-HARQ is shown in Fig. 7 in terms of the
number of TSs. As mentioned in the first paragraph of Section III, the
end-to-end packet delay represents the time duration from a packet’s
first transmission attempting until the confirmation of its successful
reception. This includes both the ‘On’ TSs and ‘Off TSs during the
transmission of a packet. Let d
d
d be a vector having the kth element d
d
d(k)
storing the recorded end-to-end delay of the kth packet. Furthermore,
let N
s
be the total number of packets successfully transmitted. Our

PMF seen in Fig. 7 for the end-to-end packet delay is formulated as
P
P
P
d
(i)=
N
s
k=1
δ (d(k) i)
N
s
, 1 i max(d
d
d). (13)
We can observe from Fig. 7 that the PMF for P
F
=0.1 has a maxi-
mum value of 0.9, meaning that 90% of the packets are successfully
transmitted with a delay of one TS. Furthermore, an additional 6% of
the packets are successfully received using two TSs. As shown in Fig
7, when P
F
increases, the PMF curves shift towards the righthand side,
implying an increase of the end-to-end packet delay.
3
6
9
12
15
Average End-to-End Delay Normalized by T
p
0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Packer Error Probability (P
F
)
P
on
= 0.0
P
on
= 0.1
P
on
= 0.2
P
on
= 0.3
P
on
= 0.4
P
on
= 0.5
P
on
= 0.6
P
on
= 0.7
P
on
= 0.8
P
on
= 0.9
Fig. 8. Average end-to-end packet delay of the CSW-HARQ scheme versus
P
F
for the various values of P
on
,whenwehaveT
s
=1T
p
and T
d
=2T
p
.
Continuing on from Fig. 7, in Fig. 8, we investigate the average end-
to-end packet delay, which is evaluated from
τ =
max(d
d
d)
i=1
P
P
P
d
(i) × i(T
s
+ T
d
)(seconds). (14)
It can be observed from Fig. 8 that the average end-to-end packet delay
increases, as P
F
and/or P
on
increase, which indicates the same trend
as that shown in Fig. 6. However, when making a close comparison
between Fig. 6 and Fig. 8, we find that the average end-to-end packet
delay is lower than the corresponding average packet delay. This is
because the packet delay includes not only the end-to-end packet delay,
but also the busy TSs before sending a new packet, which are not
accounted for the end-to-end packet delay. This also explains that at
agivenP
F
, the average end-to-end packet delay is much lower than
the corresponding average packet delay, when P
on
is relatively high,
hence resulting in numerous busy TSs.
V. C
ONCLUSIONS
In this paper, we have proposed a CSW-HARQ transmission scheme
for a CR to access a PR channel. Both the throughput and delay
performance of the proposed CSW-HARQ scheme have been inves-
tigated both by analysis and simulations. A range of formulas have
been derived and the performance of the CSW-HARQ systems has
been compared from different perspectives. Our simulation results
demonstrates that the analytical formulas are accurate. Based on
our performance results, we can conclude that the both achievable
throughput and delay performance of the CSW-HARQ is substantially
affected by both the activities of the PR and by the reliability of the CR
channels. When the PR channel is busy, the CSW-HARQ’s throughput
might become very low and its packet delay might become excessive,
even when the CR’s communication channel is reliable. Our future
research on this topic will be considering realistic imperfect sensing
scenarios as well as other types of ARQ schemes.
R
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Citations
More filters
Journal ArticleDOI
TL;DR: This survey paper provides an extensive literature review of the state-of-the-art HARQ techniques and discusses their integration in various wireless technologies, providing insights on advantages and disadvantages of particular ARQ types and discusses open problems and future directions.
Abstract: Automatic repeat request (ARQ) schemes, and in particular hybrid-ARQ (HARQ) schemes, which jointly adopt forward error correction (FEC) and ARQ, are essential to provide reliable data transmission in wireless communications systems. However, the feedback from the receiver to the transmitter and the retransmission process used in ARQ incurs significant cost in terms of power efficiency, throughput, computational power and delay. Unfortunately, such drawbacks can limit their applications to several current and emerging technologies. More specifically, the increasing number of wireless users has create spectrum scarcity, relying on small-size batteries create power constraints, deployment of real-time applications boost the demand for ultra-low delay networks, and the ultra-small low-cost Internet of Things (IoT) devices has limited signal processing and computation capabilities. Consequently, extensive research efforts have been dedicated to overcome the limitations inherent in HARQ. This survey paper provides an extensive literature review of the state-of-the-art HARQ techniques and discusses their integration in various wireless technologies. Moreover, it provides insights on advantages and disadvantages of particular ARQ types and discusses open problems and future directions.

39 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the activity of PUs, the transmission reliability of the CU, and the sensing environment have a significant impact on both the throughput and the delay of the CR system.
Abstract: The cognitive radio (CR) paradigm has the potential of improving the exploitation of the electromagnetic spectrum by detecting instantaneously unoccupied spectrum slots allocated to primary users (PUs). In order to support the process of spectrum reuse, we consider a CR scheme, which senses and opportunistically accesses a PU’s spectrum for communication between a pair of nodes relying on the stop-and-wait hybrid automatic repeat request (SW-HARQ) protocol. This arrangement is represented by the cognitive SW-HARQ (CSW-HARQ), where the availability/unavailability of the PU’s channel is modeled as a two-state Markov chain having OFF and ON states, respectively. Once the cognitive user (CU) finds that the PU’s channel is available (i.e., in the OFF state), the CU transmits data over the PU channel’s spectrum, while relying on the principles of SW-HARQ. We investigate both the throughput and the delay of CSW-HARQ, with a special emphasis on the impact of the various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Furthermore, we analyze both the throughput as well as the average packet delay and end-to-end packet delay of the CSW-HARQ system. We propose a pair of analytical approaches: 1) the probability-based and 2) the discrete time Markov chain-based. Closed-form expressions are derived for both the throughput and the delay under the perfect and imperfect sensing environments that are validated by simulation. We demonstrate that the activity of PUs, the transmission reliability of the CU, and the sensing environment have a significant impact on both the throughput and the delay of the CR system.

25 citations


Cites background or result from "Performance of Cognitive Hybrid Aut..."

  • ...This paper constitutes an evaluation of our prior contribu- 221 tions [21], [22], in which we studied both the throughput and 222 delay of CSW-HARQ, and of cognitive Go-Back-N (CGBN) 223 HARQ in the context of a CR system....

    [...]

  • ...Similar to our previous studies [21], [22], we focus 96 our attention on the opportunistic spectrum access in 97 CR systems [7], [9], where a CU senses and occupies 98 a PU’s channel for its own transmission, provided that 99 the PU’s channel is not occupied at the instant of the 100 demand [23]–[25]....

    [...]

  • ...However, in this contribution, 227 we extend the work presented in [21] to the imperfect sensing 228 environment and derived closed-form analytical expressions....

    [...]

Journal ArticleDOI
TL;DR: An algorithm is developed for deriving all the legitimate states and for eliminating the illegitimate states, which assists in reducing both the dimensionality of the state transition matrix and the associated computational complexity in the CGBN-HARQ scheme with the aid of a discrete time markov chain (DTMC).
Abstract: To mitigate spectrum scarcity, the cognitive radio (CR) paradigm has been invoked for improving the overall exploitation of the licensed spectrum by identifying and filling the free spectrum holes without degrading the transmission of primary users (PUs). Hence, we conceive a CR communication scheme, which enables a cognitive user (CU) to sense the activity of the PUs over a primary radio (PR) channel, which is exploited to transmit data using the modified Go-Back-N hybrid automatic repeat request (GBN-HARQ) protocol, when PR channel is free from the PUs. This arrangement is termed as the cognitive GBN-HARQ (CGBN-HARQ), whereby the activity of the PUs on the PR channel is modeled as a two-state Markov chain having “ ON” and “ OFF” states. However, the CU may wrongly detect the “ ON”/“ OFF” activity of the PUs in the channel, hence resulting in false-alarm or misdetection. Therefore, the two-state Markov chain is extended to four states by explicitly considering all the wrong sensing decisions. In this paper, we analytically modeled the CGBN-HARQ scheme with the aid of a discrete time markov chain (DTMC). Explicitly, an algorithm is developed for deriving all the legitimate states and for eliminating the illegitimate states, which assists us in reducing both the dimensionality of the state transition matrix and the associated computational complexity. Furthermore, based on DTMC modeling, we derive closed-form expressions for evaluating the throughput, the average packet delay, and the end-to-end packet delay of CGBN-HARQ in realistic imperfect sensing environment. The results are also validated by our simulations. Our performance results demonstrate that both the achievable throughput and the delay are significantly affected by the activity of the PUs as well as by the reliability of the PR channel and by the number of packets transmitted per time-slot (TS). To attain the maximum throughput and/or the minimum transmission delay, the number of packets transmitted within the TS should be carefully adapted based on the activity level of the PUs and on the quality of the PR channel.

13 citations


Cites background or result from "Performance of Cognitive Hybrid Aut..."

  • ...Similar to previous studied [17]–[21] and [22]–[26], the activity of the PUs is modelled using a Markov chain having the ‘ON’ and ‘OFF’ states....

    [...]

  • ...In a nutshell, in [17], [20], [21] we have studied both the throughput and delay of cognitive SW-HARQ (CSW-HARQ), cognitive Go-Back-N HARQ (CGBN-HARQ) and that of cognitive SR-HARQ (CSR-HARQ), all under the assumption of perfect spectrum sensing....

    [...]

Journal ArticleDOI
TL;DR: This paper analyzes the throughput, average packet delay, and end-to-end packets delay of the CSR-HARQ and proposes a pair of analytical approaches that rely on the classic discrete time markov chain principles.
Abstract: Dataset supporting: Ateeq Ur Rehman et al, "Performance of Cognitive Selective-Repeat Hybrid Automatic Repeat Request".In this paper, a novel transmission protocol is proposed based on the classical Selective-Repeat Hybrid Automatic Repeat to access a primary user (PU) channel, which is referred to as the CSR-HARQ. We assume that the PU transmits information based on time-slots (TSs). During a TS, the cognitive radio (CR) transmitter first senses the PU channel. Once a free TS is found, it transmits a number of packets to the CU receiver based on the principles of the SR-HARQ. In this paper, we analyze the throughput, average packet delay and end-to-end packets delay of the CSR-HARQ. We proposed a pair of analytical approaches. The first one is probability based, while the second one relies on the classic discrete time markov chain (DTMC) principles. Finally, we study the throughput, average packet delay as well as the end-to-end packet delay of the CSR-HARQ both by simulations and by evaluating our formulas. The simulation-based studies agree well with the analytical results. The performance of the CSR-HARQ systems is significantly impacted by the activity of the PU channel and by the reliability of the spectrum sensing.

12 citations


Cites methods from "Performance of Cognitive Hybrid Aut..."

  • ...Following an approach similar to our previous study in [31] and [32], the average delay TDP required for finding a free TS is mathematically expressed as...

    [...]

  • ...This paper is inspired by our own prior contributions [31]–[34], in which we studied the performance of the Cognitive Stop-and-Wait HARQ (CSW-HARQ) and Cognitive Go-Back-N HARQ (CGBN-HARQ), when both reliable and realistic imperfect sensing are assumed....

    [...]

  • ...All the free as well as busy TSs commencing from the time the CR system is activated are included in the average packet delay quantified in terms of the number of TSs per packet [31], [32]....

    [...]

  • ...Specifically, in [31] and [32], we studied the performance of the CSW-HARQ protocol, which enables the CU transmitter to transmit a single packet in each free TS and waits for its feedback assumed to be received within the same TS....

    [...]

  • ...Similar to our previous studies [31]–[34], the activity of PU is modelled using a two-state Discrete Time Markov chain (DTMC), having ‘ON’ and ‘OFF’ states [35], [36]....

    [...]

Proceedings ArticleDOI
15 May 2016
TL;DR: This paper investigates both the throughput and delay of CGBN-HARQ, with a special emphasis on the impact of various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing.
Abstract: In this paper, we propose a cognitive Go-Back-N Hybrid Automatic Repeat reQuest (CGBN-HARQ) scheme for a cognitive radio (CR) system to opportunistically transmit data over a primary radio (PR) channel. We model the activity of PR users (PRUs) occupying the PR channel as a Markov chain with two states: `ON' and `OFF'. In order to use the PR channel, the CR system first senses the availability/unavailability of the PR channel. Once it finds that the PR channel is free, the CR system transmits data packets over the PR channel's spectrum, whilst relying on the principles of GBN-HARQ. In this paper, we investigate both the throughput and delay of CGBN-HARQ, with a special emphasis on the impact of various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Our studies demonstrate that the activity of PRUs, the transmission reliability of the CR system as well as the number of packets transmitted per time-slot may have a substantial impact on both the throughput and the delay of the CR system.

10 citations


Cites background or methods from "Performance of Cognitive Hybrid Aut..."

  • ...As in [5], we consider a PR channel, which is used by the PRUs accessing it based on TSs of duration T ....

    [...]

  • ...In [5], we have proposed a Cognitive Stop-and-Wait Hybrid Automatic Repeat reQuest (CSW-HARQ) scheme for opportunistically accessing a PRU’s channel, and studied both the attainable throughput and the delay imposed by cognitive Stop-and-Wait-HARQ (CSWHARQ) scheme....

    [...]

  • ...Following on from our studies in [5], in this paper, we propose a Cognitive Go-Back-N HARQ (CGBN-HARQ) scheme and investigate both its throughput and delay....

    [...]

  • ...As in [5], we assume that PRUs activate a PR channel according to a two-state Markov chain with the states ‘ON’ and ‘OFF’ [6]....

    [...]

References
More filters
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Simon Haykin1
TL;DR: Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks: radio-scene analysis, channel-state estimation and predictive modeling, and the emergent behavior of cognitive radio.
Abstract: Cognitive radio is viewed as a novel approach for improving the utilization of a precious natural resource: the radio electromagnetic spectrum. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: /spl middot/ highly reliable communication whenever and wherever needed; /spl middot/ efficient utilization of the radio spectrum. Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks. 1) Radio-scene analysis. 2) Channel-state estimation and predictive modeling. 3) Transmit-power control and dynamic spectrum management. This work also discusses the emergent behavior of cognitive radio.

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"Performance of Cognitive Hybrid Aut..." refers methods in this paper

  • ...Specifically, in our studies, the activity of a PR channel is modelled using a two-state Markov chain [15], with the two states representing the ‘On’ and ‘Off’ status of PRUs....

    [...]

  • ...In order to analyze and detect the activity of PRUs on a channel, a number of sensing techniques were proposed in the literature [5], [11]–[14]....

    [...]

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  • ...A CR is capable of detecting the unoccupied portions of the licensed spectrum and of efficiently accessing them for its own data transmission without affecting the legal rights of PRUs [8], [9]....

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Journal ArticleDOI
TL;DR: With RKRL, cognitive radio agents may actively manipulate the protocol stack to adapt known etiquettes to better satisfy the user's needs and transforms radio nodes from blind executors of predefined protocols to radio-domain-aware intelligent agents that search out ways to deliver the services the user wants even if that user does not know how to obtain them.
Abstract: Software radios are emerging as platforms for multiband multimode personal communications systems. Radio etiquette is the set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes. Cognitive radio enhances the flexibility of personal services through a radio knowledge representation language. This language represents knowledge of radio etiquette, devices, software modules, propagation, networks, user needs, and application scenarios in a way that supports automated reasoning about the needs of the user. This empowers software radios to conduct expressive negotiations among peers about the use of radio spectrum across fluents of space, time, and user context. With RKRL, cognitive radio agents may actively manipulate the protocol stack to adapt known etiquettes to better satisfy the user's needs. This transforms radio nodes from blind executors of predefined protocols to radio-domain-aware intelligent agents that search out ways to deliver the services the user wants even if that user does not know how to obtain them. Software radio provides an ideal platform for the realization of cognitive radio.

9,238 citations


"Performance of Cognitive Hybrid Aut..." refers background in this paper

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Journal ArticleDOI
TL;DR: In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented and the cooperative sensing concept and its various forms are explained.
Abstract: The spectrum sensing problem has gained new aspects with cognitive radio and opportunistic spectrum access concepts. It is one of the most challenging issues in cognitive radio systems. In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented. Various aspects of spectrum sensing problem are studied from a cognitive radio perspective and multi-dimensional spectrum sensing concept is introduced. Challenges associated with spectrum sensing are given and enabling spectrum sensing methods are reviewed. The paper explains the cooperative sensing concept and its various forms. External sensing algorithms and other alternative sensing methods are discussed. Furthermore, statistical modeling of network traffic and utilization of these models for prediction of primary user behavior is studied. Finally, sensing features of some current wireless standards are given.

4,812 citations

Book
01 Jan 1983
TL;DR: This book explains coding for Reliable Digital Transmission and Storage using Trellis-Based Soft-Decision Decoding Algorithms for Linear Block Codes and Convolutional Codes, and some of the techniques used in this work.
Abstract: 1. Coding for Reliable Digital Transmission and Storage. 2. Introduction to Algebra. 3. Linear Block Codes. 4. Important Linear Block Codes. 5. Cyclic Codes. 6. Binary BCH Codes. 7. Nonbinary BCH Codes, Reed-Solomon Codes, and Decoding Algorithms. 8. Majority-Logic Decodable Codes. 9. Trellises for Linear Block Codes. 10. Reliability-Based Soft-Decision Decoding Algorithms for Linear Block Codes. 11. Convolutional Codes. 12. Trellis-Based Decoding Algorithms for Convolutional Codes. 13. Sequential and Threshold Decoding of Convolutional Codes. 14. Trellis-Based Soft-Decision Algorithms for Linear Block Codes. 15. Concatenated Coding, Code Decomposition ad Multistage Decoding. 16. Turbo Coding. 17. Low Density Parity Check Codes. 18. Trellis Coded Modulation. 19. Block Coded Modulation. 20. Burst-Error-Correcting Codes. 21. Automatic-Repeat-Request Strategies.

3,848 citations

Journal ArticleDOI
TL;DR: An overview of challenges and recent developments in both technological and regulatory aspects of opportunistic spectrum access (OSA) is presented, and the three basic components of OSA are discussed.
Abstract: Compounding the confusion is the use of the broad term cognitive radio as a synonym for dynamic spectrum access. As an initial attempt at unifying the terminology, the taxonomy of dynamic spectrum access is provided. In this article, an overview of challenges and recent developments in both technological and regulatory aspects of opportunistic spectrum access (OSA). The three basic components of OSA are discussed. Spectrum opportunity identification is crucial to OSA in order to achieve nonintrusive communication. The basic functions of the opportunity identification module are identified

2,819 citations


"Performance of Cognitive Hybrid Aut..." refers background in this paper

  • ...This inefficient spectrum exploitation motivates the concept of dynamic spectrum access, which allows cognitive radio users (CRUs) to access and utilize the unoccupied spectrum holes, which have traditionally been exclusively assigned to primary radio users (PRUs) [5], [6]....

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Frequently Asked Questions (2)
Q1. What are the contributions mentioned in the paper "Performance of cognitive hybrid automatic repeat request: stop-and-wait" ?

In this paper, the authors consider a CR scheme, which opportunistically accesses a PR channel for communication between a pair of nodes based on the stop-and-wait hybrid automatic repeat request ( SW-HARQ ). In this paper, the authors analyze both the throughput and delay performance of the CSW-HARQ system, for which a range of closed-form formulas are derived that are also validated by simulation results. 

Their future research on this topic will be considering realistic imperfect sensing scenarios as well as other types of ARQ schemes.