Rex: A randomized EXclusive region based scheduling scheme for mmWave WPANs with directional antenna
SummaryΒ (3 min read)
Introduction
- The mmWave communications have many salient features.
- To ensure the success of mmWave based WPANs, how to efficiently and effectively allocate resource for co-existing mmWave devices is a critical issue, which is the main focus of this paper.
- Extensive simulations have demonstrated the accuracy of the analysis and the efficiency of the proposed scheduling scheme.
A. mmWave Channel Characteristics and Multiple Access
- The main characteristics of mmWave communications are short wavelength/high frequency, large bandwidth and high interaction with atmospheric constituents.
- Orthogonal frequency-division multiplexing (OFDM) signals are relatively robust against ISI due to the reduced symbol rate in each of the subcarriers, and thus, it is a good candidate for mmWave communications.
- OFDM can be combined with a multiple access scheme such as Time Division Multiplex Access (TDMA) or Code Division Multiple Access (CDMA) for effective multiple access control [4].
- For RF oscillators at mmWave spectrum, it is very difficult to maintain a low level phase noise, which affects the signal in the frequency conversion operations, and results in higher bit error rate (BER) for effective communications.
- According to [6], MC-DS-CDMA is most robust against phase noise and multiple access interference (MAI).
B. Directional Antennae
- Because of the unique characteristics of 60 GHz mmWave communications, i.e., small wavelength and high path loss due to severe oxygen absorption and atmospheric attenuation, it is highly desired to use directional antenna to achieve much higher antenna gain over a longer transmission range, by radiating transmission energy to the desired direction only [7].
- There are two types of directional antennae [8]: conventional sectored/switched antenna array and adaptive antenna array.
- In a mmWave WPAN with directional antennae, directivity and high path loss should result in a more efficient spectrum reuse and significant improvement in the network throughput.
- In addition, directional antennae are more energy efficient.
- A more realistic three-dimensional cone plus sphere model is proposed in [11], taking the effects of sidelobes into consideration.
C. WPAN Network Architecture
- IEEE 802.15.3 is the standard dedicated for high rate WPANs.
- According to IEEE 802.15.3, multiple devices form a piconet which is the basic network element.
- Data transmissions in the piconet is based on the time-slotted superframe structure [12].
- The PNC broadcasts beacons periodically to all directions which allow other devices to synchronize and determine their locations.
- The scheduling algorithm is not specified in the standard, and it is their focus.
III. EXCLUSIVE REGIONS
- Let ππ denote the received signal power, π the channel capacity (or the achievable data rate with an efficient transceiver design), π0 the one-sided spectral density of white Gaussian noise, and πΌ the total interference power.
- Authorized licensed use limited to: UNIVERSITY OF VICTORIA.
- Assume that πΊπ (π), πΊπ (π) and πΌ are constant, and all devices use the same transmission power.
- Nevertheless, the previous derived sufficient condition can still ensure that π π β€ π β²π. If πΌπ,π β€ π0π , 1The necessary and sufficient condition to ensure that π β²π β₯.
A. REX Scheme
- It is shown in Sec. III that concurrent transmissions are more favorable than serial TDMA transmissions if all interfering devices are sufficiently far apart, i.e., outside the ERs of the other receivers.
- In the following, the authors propose REX, a randomized ER based scheduling scheme for a centralized mmWave WPAN, with computational complexity π(π2 logπ) to allocate a time slot.
- If the flow is not included in πΉπ, add it to πΉπ; β Step 2: Check all the remaining active flows in the set π{π} β πΎπ for concurrent transmission conditions as derived in (6)-(14), starting from the flow with the smallest ππ.
- If the authors search 2In WPANs, the mobility is typically low, e.g., β€ 1 m/s, and the superframe duration is less than 100 ms.
- Authorized licensed use limited to: UNIVERSITY OF VICTORIA.
B. Average Number of Concurrent Transmissions
- Consider an πΏΓπΏ square room containing π active flows, with π transmitters and π receivers randomly deployed.
- Due to the omni- receivers and directional transmitters, the ER in case 2 contains two zones, a circle with radius π1 and another circle with radius π2, as shown in Fig. 2(b).
- Thus, the developed analytical model without considering the edge effect may result in a conservative estimation of πΈ[πΆπ ].
V. PERFORMANCE EVALUATION
- The authors calculate the analytical results using Maple 10 [14] and compare the network performance of the proposed REX scheme with TDMA through extensive simulations using C.
- The authors repeat the simulation 500 times with different random seeds and calculate the average value.
A. Spatial multiplexing gain
- The relationship between the number of concurrent transmissions and path loss exponent πΌ is shown in Fig.
- Higher interference among these flows may limit the network throughput.
- The results demonstrate the effectiveness and efficiency of the REX scheme.
- Fig. 5(b) shows the spatial multiplexing gains obtained in cases 2-4.
- The results are shown in Fig. 6, with the cone plus circle model introduced in Sec. II-B.
C. Fairness
- The fairness of REX and TDMA are first measured by Jainβs fairness index [15], ( β π₯π) 2/(π β π₯2π ), in terms of the total number of time slots allocated to each flow.
- As shown in Fig. 8 (a), with the deterministic searching sequence, fairness degrades drastically when the number of flows increases, while the proposed REX scheduling scheme using sorted searching sequence can achieve better fairness, regardless of the number of flows.
- The authors compare the per-flow throughput of REX and TDMA, and the maximum and minimum per-flow throughputs are shown in Fig.
- Among the 40 flows, when the beamwidth Authorized licensed use limited to: UNIVERSITY OF VICTORIA.
VII. CONCLUSION
- The authors have obtained the sufficient conditions in terms of ERs to ensure that the concurrent transmission scheme can outperform the TDMA scheme, considering both omni- and directional antennae.
- In addition, the authors have proposed the REX scheduling scheme, and derived the average number of concurrent transmissions given the ER condition.
- By scheduling appropriate concurrent transmissions, significant spatial multiplexing gain can be achieved, especially for mmWave WPANs with directional antennae.
- The authors have used the transceiver distance to estimate the average received signal strength and interference level without considering fast fading.
- This is because the transmissions scheduled in WPANs are peer-to-peer transmissions, and it is very costly to measure their instantaneous channel quality.
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Citations
1,041Β citations
Cites background from "Rex: A randomized EXclusive region ..."
...REX [69] Yes, based on IEEE 802....
[...]
...[69] introduced the concept of exclusive region (ER) to enable concurrent transmissions, and derived the ER conditions that concurrent transmissions always outperform TDMA for both omni-antenna and directional-antenna models....
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375Β citations
Cites background from "Rex: A randomized EXclusive region ..."
...In [13], an exclusive region (ER)-based resource management scheme is proposed to exploit the spatial reuse, and the optimal ER sizes are derived....
[...]
...Several works on directional mmWave MAC for networks with low user mobility (e.g., WLAN or WPAN) have appeared in the literature [12, 13]....
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200Β citations
Cites methods from "Rex: A randomized EXclusive region ..."
... work on directional MAC protocols for mmWave communications. Since TDMA is adopted in ECMA-387 [6], IEEE 802.15.3c [8], and IEEE 802.11ad [9], many protocols are based on TDMA [67], [68]. Cai et al. [69] introduced the concept of exclusive region (ER) to enable concurrent transmissions, and derived the ER conditions that concurrent transmissions always outperform TDMA for both omni-antenna and direct...
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...eciο¬ed distributed FDMAC [62] No, frame-based supported, by greedy coloring (GC) algorithm not speciο¬ed centralized D-CoopMAC [75] No, based on IEEE 802.11ad not speciο¬ed not speciο¬ed centralized REX [69] Yes, based on IEEE 802.15.3 supported, by a randomized ER based scheduling scheme not speciο¬ed centralized Spatial sharing [66] No, based on IEEE 802.11ad supported, based on the BF information not s...
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189Β citations
Cites background from "Rex: A randomized EXclusive region ..."
...For the THF band, water vapor serves the role of primary absorbent [13], [14]....
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160Β citations
References
14,065Β citations
"Rex: A randomized EXclusive region ..." refers background in this paper
...There are two types of directional antennae [8]: conventional sectored/switched antenna array and adaptive antenna array....
[...]
9,008Β citations
"Rex: A randomized EXclusive region ..." refers background in this paper
...Without rate adaptation, the ER in [18] is a function of distance between the transceivers, which is different from the ER we discussed....
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...In [18], to quantify wireless network capacity, a protocol model was proposed for communications without rate adaptation, and an exclusive region concept was given....
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2,137Β citations
"Rex: A randomized EXclusive region ..." refers background in this paper
...Several combinations of OFDM and CDMA have been discussed in [5]....
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680Β citations
"Rex: A randomized EXclusive region ..." refers background in this paper
...A more realistic three-dimensional cone plus sphere model is proposed in [11], taking the effects of sidelobes into consideration....
[...]
488Β citations
"Rex: A randomized EXclusive region ..." refers methods in this paper
...The fairness of REX and TDMA are first measured by Jainβs fairness index [15], ( β xi) (2)/(N β x(2)i ), in terms of the total number of time slots allocated to each flow....
[...]