Showing papers by "Raymond Knopp published in 2012"

Contention Based Access for Machine-Type Communications over LTE

Abstract: To enable the efficient and low latency machine-type communications (MTC) over long term evolution (LTE), a contention based access (CBA) method is proposed. With CBA, UEs transmit packets on the randomly selected resource without having any UE specific scheduled resources. To address the problem of collision caused by CBA in high traffic load, eNB exploits the MU-MIMO detection technique to decode radio network temporary identifier (RNTI) of the collided UEs and use this information to perform a regular scheduling in subsequent subframe. Detailed low layer signaling enhancement to implement CBA technique in current LTE specification (Rel. 10) is also presented. Simulation results demonstrate that the CBA significanlty outperforms the existing uplink channel access methods.

Adaptive modulation and coding with Hybrid-ARQ for latency-constrained networks

Abstract: Traffic generated by machine to machine (M2M) communication or online gaming will be a large and integral part of the traffic transported by LTE-advanced and beyond networks. This traffic is characterized by sporadic and low-throughput packet arrivals. It must be scheduled under a latency constraint. Sporadic traffic creates environments where the channel-quality information (CQI) is outdated or unavailable. Fast-fading, the non-stationarity of inter-cell interference and the heterogeneity of Rel-10 networks further exacerbates this issue. However, current LTE-Advanced schedulers and resource allocation schemes are not optimized for these particular scenarios. In this paper, we propose a scheduling and resource allocation mechanism for latency-constrained operation. Our solution significantly improves the spectral efficiency of delay-constrained networks by optimizing a joint hybrid-ARQ and adaptive modulation and coding (AMC) policy that changes the number of dimensions (physical resources) used in each round. With only one bit of feedback, obtained causally from hybrid-ARQ, we achieve a performance close to the ergodic capacity.

Interference Suppression Strategy for Cell-Edge Users in the Downlink

Abstract: In this paper we focus on the cell-edge users whose performance is severely limited by the interfering signals of diverse rates and strengths In contrast to the suboptimal single-user detection, we propose an interference suppression strategy based on a low complexity matched filter (MF) based receiver This proposed receiver exploits the structure of dominant interference in the detection process, instead of assuming it to be Gaussian and merging it in noise This receiver is also characterized by the reduction of one complex dimension in the detection process thereby making it low complexity receiver structure For comparison purposes, we also include the analysis of MMSE receiver and show that while MMSE detection loses one diversity order in the presence of one interferer, the proposed receiver recuperates the lost order of diversity We further show that MMSE detection suffers from a coding loss as the interference gets stronger while the proposed receiver exhibits a coding gain as either the interference gets stronger or its modulation order decreases Based on these results, we further propose a novel fractional frequency reuse (FFR) scheme for cellular systems

Link abstraction for multi-user MIMO in LTE using interference-aware receiver

Abstract: Most of the recent wireless communication systems are interference limited rather than noise limited. In the case of a very strong interferer the conventional assumption of the interference as Gaussian is extremely suboptimal. However optimal (capacity achieving) receivers utilize some prior knowledge about the interference to reach optimality. The link abstraction for such receiver structures is not studied well. We investigate how the conventional mutual information based link abstraction technique can be extended for the accurate and efficient link performance modeling for low complexity optimal receivers. So, in this paper we propose a mutual information based link abstraction methodology of an optimal, low complexity interference aware receiver for multi-user MIMO in the frame work of LTE. For the sake of comparison we performed abstraction of interference aware receiver with Exponential Effective SINR Mapping (EESM) method as well. We show with the help of results that our proposed method outperforms the EESM and provides the system level with more accurate link quality metric.

Towards integrating Quantize-Map-Forward relaying into LTE

Abstract: We present a method to integrate the Quantize-Map-Forward (QMF) relaying scheme [1] into the standard LTE operation, for a two-relay diamond network configuration. Our approach implements QMF using mainly existing LTE modules and functionalities, and results in minimal changes in the standard link-layer LTE operation. In particular, the destination operation is only affected in that we adapt the log-likelihood ratio (LLR) calculations at the decoder input to take into account the existence of relays; thus, the decoding complexity and operations (apart the LLR calculations) are not modified. We report extensive performance evaluations of our scheme using the OpenAirInterface (OAI) link-level simulation tools.

Flexible front-end processing for software defined radio applications using application specific instruction-set processors

Abstract: High computational demands of today's wireless communication standards require the design of highly flexible Software Defined Radio (SDR) platforms like the OpenAirInter-face ExpressMIMO platform. A DSP engine of major importance is the Front-End Processor (FEP) which deals with the different air-interface operations at the transceiver side. In this paper we propose an Application Specific Instruction-Set Processor (ASIP) architecture for front-end processing and compare it to a programmable DSP engine as well as to other ASIP solutions. For design comparison we mainly focus on architectural differences and the runtime performance in terms of processing time. The synthesis results are provided for different target technologies.

Software implementation of spatial interweave cognitive radio communication using OpenAirInterface platform

Abstract: We present in this paper a software implementation of a cognitive radio (CR) communication based on long term evolution-time division duplex (LTE-TDD) channel reciprocity. We study the problem of calibration and beamforming design for a CR system in which a multiple-input single-output (MISO) secondary link, wants to opportunistically communicate without harming the primary SISO system. Specifically, we evaluate the CR communication through the EURECOM's experimental OpenAirInterface (OAI) software platform. We will show that it is feasible to restore the reciprocity after calibration in a non reciprocal channel, and provide an overview of challenges in the channel estimation for real conditions.

Cooperative communications with HARQ in a wireless mesh network based on 3GPP LTE

Abstract: This paper presents some results of the FP7 ICT-LOLA (achieving LOw LAtency in wireless communications) project on the design of a clusterized wireless mesh network based on 3GPP LTE. First, we focus on the new MAC/PHY structure proposed. Then, the concept of virtual link is presented for inter-cluster communications combining MAC layer forwarding, hybrid automatic repeat request (HARQ) and cooperative communications with Decode and Forward (DF). The goal of a virtual link is to enable low latency data transfer in inter-cluster communications. The virtual link solution is studied by simulations thanks to OpenAirInterface which integrates LTE MAC and PHY layer procedures, as well as adaptations needed for the LOLA wireless mesh network. Simulation results show that the proposed distributed solution smoothly adapts to the link conditions. A loss in throughput efficiency is the price to be paid in certain configurations for the distributed operation of the virtual link. Nevertheless, the technique helps in reducing the average number of transmissions thus contributing to improve the latency of the system.

Dynamic Power Management for the Iterative Decoding of Turbo Codes

Abstract: Turbo codes are presently ubiquitous in the context of mobile wireless communications among other application domains. A decoder for such codes is typically the most power intensive component in the baseband processing chain of a wireless receiver. The iterative nature of these decoders represents a dynamic workload. This brief presents a dynamic power management policy for these decoders. An algorithm is proposed to tune a power manageable decoder according to a prediction of the workload involved within the decoding task. By reclaiming the timing slack left when operating the decoder at a high power mode, the proposed algorithm continuously looks for opportunities to switch to a lower power mode that guarantees the task completion. We apply this technique to an long term evolution Turbo decoder and explore the feasibility of a VLSI implementation on a CMOS technology of 65 nm. Energy savings of up to 54% were achieved with a relatively low loss in error-correction performance.

Interference alignment for achieving both full DoF and full diversity in the broadcast channel with delayed CSIT

Abstract: Maddah-Ali and Tse have recently shown that delayed transmitter channel state information (CSIT) can still be useful in increasing the degrees-of-freedom (DoF) over the MIMO broadcast channel. This was achieved by constructing a scheme that, in the presence of two transmit antennas, of two single-antenna receivers, and of CSIT that is delayed by one coherence time, manages to provide each user with 2/3 DoF, improving upon the 1/2 DoF corresponding to no CSIT. This same scheme though, as well as all subsequent schemes pertinent schemes, achieve DoF gains by suppressing the inherent diversity of the broadcast parallel channel. The current work proposes a novel broadcast scheme which, over the above described setting of the delayed CSIT broadcast channel, employs a form of interference alignment to achieve both full DoF as well as full diversity.

On the Capacity of the Two-user Gaussian Causal Cognitive Interference Channel

Abstract: This paper considers the two-user Gaussian Causal Cognitive Interference Channel (GCCIC), which consists of two source-destination pairs that share the same channel and where one full-duplex cognitive source can causally learn the message of the primary source through a noisy link. The GCCIC is an interference channel with unilateral source cooperation that better models practical cognitive radio networks than the commonly used model which assumes that one source has perfect non-causal knowledge of the other source's message. First the sum-capacity of the symmetric GCCIC is determined to within a constant gap. Then, the insights gained from the derivation of the symmetric sum-capacity are extended to characterize the whole capacity region to within a constant gap for more general cases. In particular, the capacity is determined (a) to within 2 bits for the fully connected GCCIC when, roughly speaking, the interference is not weak at both receivers, (b) to within 2 bits for the Z-channel, i.e., when there is no interference from the primary user, and (c) to within 2 bits for the S-channel, i.e., when there is no interference from the secondary user. The parameter regimes where the GCCIC is equivalent, in terms of generalized degrees-of-freedom, to the noncooperative interference channel (i.e., unilateral causal cooperation is not useful), to the non-causal cognitive interference channel (i.e., causal cooperation attains the ultimate limit of cognitive radio technology), and to bilateral source cooperation are identified. These comparisons shed lights into the parameter regimes and network topologies that in practice might provide an unbounded throughput gain compared to currently available (non cognitive) technologies.

IEEE 802.11p Receiver Design for Software Defined Radio Platforms

Abstract: Software Defined Radio platforms are a flexible and cost efficient solution to deal with the increasing number of today's wireless communication standards. One interesting use case can be found in the automotive industry where the IEEE 802.11p standard enables Car-to-Car and Car-to-Infrastructure communication. In the context of this paper we present a physical layer implementation of the 802.11p receiver for the OpenAirInterface ExpressMIMO platform. Our results show that a real-time processing is already possible for most of the modulation schemes when applying a centralized control flow. The results are further extended by recommendations of further design improvements and the derivation of general guidelines for further standard deployment on the platform.

Low-latency transmission of low-rate analog sources

Abstract: Asymptotically optimal schemes for both single and dual-source cases with low-latency are addressed in this research. Single-source two-way protocol with non-coherent reception is introduced and its asymptotic behaviour is studied. The protocol consists of a data phase and a control phase which can go on up to N rounds. An upper bound on the distortion is derived for a two-round protocol. It is also extended to the case where there are two highly correlated analog sources one of which is uniformly distributed and the other one with a contaminated uniform distribution in the presence of two-sided feedback. Total energy used by protocol is fixed and the energy used by each source in both phases are derived individually. We have shown that it is possible to achieve the distortion bound of the single-source with two highly correlated sources in two rounds.

On the Two-user Gaussian Causal Cognitive Interference Channel

Abstract: This paper considers the two-user Gaussian Causal Cognitive Interference Channel (G-CCIC). The G-CCIC consists of two full-duplex transmitter-receiver pairs that share the same channel and where one transmitter can causally learn the message of the other transmitter through a noisy link. The G-CCIC is an interference channel with unilateral source cooperation that better models practical cognitive radio networks than the classical cognitive channel where one transmitter is assumed to know the message of the other transmitter anti-causally. The sum-capacity of the G-CCIC is studied in both the interference symmetric and interference asymmetric cases. In the former case the two interfering links and the two direct links are of the same strength, in the latter case one of the interfering links is set to zero. It is shown through evaluation of various achievable schemes that known sum-rate upper-bounds are achievable to within a constant gap regardless of the channel parameters. Interestingly, except for a small set of parameters, the achievable schemes are quite simple in the sense that only superposition coding is used. More complex schemes based on binning and superposition coding are shown to achieve a smaller gap than superposition coding alone. Finally, the parameter regimes where G-CCIC is equivalent in terms of generalized degrees-of-freedom to no-cooperation (i.e., causal cooperation is not useful), to non-causal cooperation (i.e., causal cooperation attains the ultimate limit of source cooperation), and to bilateral source cooperation are identified.

Interference relay channel in 4G wireless networks

Abstract: In the next generation cellular systems, such as LTE-A (Release 10 and beyond), relay node (RN) deployment has been adopted due to its potentials in enlarging coverage and increasing system throughput, even with primitive relaying functionalities. For example, in LTE-A Release 10 only Type-I (non-transparent) RNs are considered wherein no cooperative transmission to the Donor evolved-NodeBs (DeNBs) is allowed. In this paper, we would like to add more functionalities to the RNs and see the advantages of using cooperative relaying, i.e., Type-II RNs. In particular, we study an interference relay channel (IRC) consisting of two single-antenna transmitter-receiver pairs and a shared multiple-antenna RN, which is exploited in a way that interferer's signal components at each receiver node are eliminated. Specifically, at the RN a transmit filtering is performed such that the compound received signal at each user equipment (UE) has a structure similar to the receiver structure for Alamouti's space-time coding [1]. We also show that it is not always required to have more complex receiver structure at the RN in order to achieve better spectral efficiencies.

Adaptive transmission and multiple-access for sparse-traffic sources

Abstract: M2M/online gaming are considered as key applications in LTE and LTE-advanced networks. However, for most of these applications whose traffic is sporadic and some of them require very low latency, they are not well supported by the current LTE and LTE-advanced systems due to the large signaling overhead. This paper proposes two methods to address this problem. The first method provides a co-optimization method for AMC and HARQ when CQI is outdated or unavailable and there is a latency constraint. The second method presents a contention based access method to reduce uplink channel access latency. Simulation results show that with these two methods a significant improvement in spectral efficiency can be achieved while greatly reducing latency or maintaining a latency constraint.