Youguang Zhang

FASA: accelerated S-ALOHA using access history for event-driven M2M communications

Supporting massive device transmission is challenging in machine-to-machine (M2M) communications. Particularly, in event-driven M2M communications, a large number of devices become activated within a short period of time, which in turn causes high radio congestions and severe access delay. To address this issue, we propose a Fast Adaptive S-ALOHA (FASA) scheme for random access control of M2M communication systems with bursty traffic. Instead of the observation in a single slot, the statistics of consecutive idle and collision slots are used in FASA to accelerate the tracking process of network status that is critical for optimizing S-ALOHA systems. With a design based on drift analysis, the estimate of the number of the active devices under FASA converges fast to the true value. Furthermore, by examining the T-slot drifts, we prove that the proposed FASA scheme is stable as long as the average arrival rate is smaller than e-1, in the sense that the Markov chain derived from the scheme is geometrically ergodic. Simulation results demonstrate that under highly bursty traffic, the proposed FASA scheme outperforms traditional additive schemes such as PB-ALOHA and achieves near-optimal performance in reducing access delays. Moreover, compared to multiplicative schemes, FASA shows its robustness under heavy traffic load in addition to better delay performance.

Directional Cooperative MAC Protocol Design and Performance Analysis for IEEE 802.11ad WLANs

In this paper, we consider the directional multigigabit (DMG) transmission problem in IEEE 802.11ad wireless local area networks (WLANs) and design a random-access-based medium access control (MAC) layer protocol incorporated with a directional antenna and cooperative communication techniques. A directional cooperative MAC protocol, namely, D-CoopMAC, is proposed to coordinate the uplink channel access among DMG stations (STAs) that operate in an IEEE 802.11ad WLAN. Using a 3-D Markov chain model with consideration of the directional hidden terminal problem, we develop a framework to analyze the performance of the D-CoopMAC protocol and derive a closed-form expression of saturated system throughput. Performance evaluations validate the accuracy of the theoretical analysis and show that the performance of D-CoopMAC varies with the number of DMG STAs or beam sectors. In addition, the D-CoopMAC protocol can significantly improve system performance, as compared with the traditional IEEE 802.11ad MAC protocol.

Fast Adaptive S-ALOHA Scheme for Event-Driven Machine-to-Machine Communications

Machine-to-Machine (M2M) communication is now playing a market-changing role in a wide range of business world. However, in event-driven M2M communications, a large number of devices activate within a short period of time, which in turn causes high radio congestions and severe access delay. To address this issue, we propose a Fast Adaptive S- ALOHA (FASA) scheme for M2M communication systems with bursty traffic. The statistics of consecutive idle and collision slots, rather than the observation in a single slot, are used in FASA to accelerate the tracking process of network status. Furthermore, the fast convergence property of FASA is guaranteed by using drift analysis. Simulation results demonstrate that the proposed FASA scheme achieves near-optimal performance in reducing access delay, which outperforms that of traditional additive schemes such as PB-ALOHA. Moreover, compared to multiplicative schemes, FASA shows its robustness even under heavy traffic load in addition to better delay performance.

Time—frequency iterative multiuser detection in time—frequency‐domain spread multicarrier DS‐CDMA systems over Nakagami‐m fading channels

In this paper, we propose and study a novel Time–frequency-domain iterative multiuser detector (TF-IMUD) for the multicarrier direct-sequence code-division multiple-access (DS-CDMA) systems employing both time (T)-domain and frequency (F)-domain spreading, which, for brevity, are referred to as the TF/MC DS-CDMA systems. This novel TFIMUD consists of a set of T-domain soft-input soft-output MUDs (SISO-MUDs) and a set of F-domain SISO-MUDs, where information is exchanged between the T-domain and F-domain through two multiuser interference (MUI) cancellation units. The T-domain and F-domain SISO-MUDs are operated under the maximum likelihood (ML) principles, and they are facilitated to be implemented using parallel signal processing techniques. In this paper, the complexity of the TF-IMUD and the bit error rate (BER) performance of the TF/MC DS-CDMA systems employing the proposed TF-IMUD are investigated and also compared with the other existingMUDschemes, including the optimum ML-MUD and the joint/separate minimum mean-square error (MMSE)-MUDs. Our study and simulation results showthat the TF-IMUD is capable of achieving nearly the same BER performance as the optimum ML-MUD, but at significantly lower complexity.

Application-level scheduling with deadline constraints

Opportunistic scheduling of delay-tolerant traffic has been shown to substantially improve spectrum efficiency. To encourage users to adopt delay-tolerant scheduling for capacity-improvement, it is critical to provide guarantees in terms of completion time. In this paper, we study application-level scheduling with deadline constraints, where the deadline is pre-specified by users/applications and is associated with a deadline violation probability. To address the exponentially-high complexity due to temporally-varying channel conditions and deadline constraints, we develop a novel asymptotic approach that exploits the largeness of the network to our advantage. Specifically, we identify a lower bound on the deadline violation probability, and propose simple policies that achieve the lower bound in the large-system regime. The results in this paper thus provide a rigorous analytical framework to develop and analyze policies for application-level scheduling under very general settings of channel models and deadline requirements. Further, based on the asymptotic approach, we propose the notion of Application-Level Effective Capacity region, i.e., the throughput region that can be supported subject to deadline constraints, which allows us to quantify the potential gain of application-level scheduling.

On the Asymptotic Spectral Efficiency of Uplink MIMO-CDMA Systems Over Rayleigh Fading Channels With Arbitrary Spatial Correlation

In this paper, we study the asymptotic spectral efficiency (ASE) of the uplink multiple-input-multiple-output direct-sequence code-division multiple-access (MIMO-CDMA) systems supporting multiple users, when assuming communications over flat-fading channels with arbitrary correlation in the spatial domain. In the MIMO-CDMA systems considered, the system-channel-related matrix expressed by H is a block random matrix, whose entries may be correlated due to the spatial correlation. In this paper, the theory of operator-valued free probability is employed to derive the approximate asymptotic eigenvalue distribution (AED) of the correlation matrix RH = HH H, where the size of the block matrix H tends to infinity. Based on the approximate AED, the spectral efficiency (SE) performance of multiuser MIMO-CDMA systems is studied by both analysis and simulations. Our simulation and numerical results show that the corresponding ASE is, in general, capable of providing very good prediction of the SE achieved by the practical MIMO-CDMA systems.

Capacity of generalised network multiple-input–multiple-output systems with multicell cooperation

In network multiple-input–multiple-output (MIMO) systems, cooperative base stations (BSs) and mobile terminals (MTs) are in general at different geographic locations. Correspondingly, the channel gains with respect to different BSs and/or MTs may obey different distributions, which resulted from, different pathlosses, different strength of line-of-sight (LOS) components and so on. Furthermore, future wireless communication systems are expected to be equipped with multiple antennas for transmission/receiving. In these multiantenna systems, signals received by the antennas of one BS from one MT may be correlated. Against the above-mentioned scenarios, in this contribution, the authors study the capacity of the generalised uplink network MIMO systems with multicell cooperation (MCoP), when propagation pathlosses, fast Rician fading with various LOS components and spatial correlation are simultaneously considered. Specifically, the theory of operator-valued free probability is introduced to derive the approximate eigenvalue distribution (AED) of the correlation matrix of the equivalent channels. Based on the AED, the approximate capacity of uplink network MIMO systems is then studied. Furthermore, a range of special cases are analysed by specialise the authors model and modifying their results. Finally, both numerical and simulation results are provided for characterising the capacity of network MIMO systems with MCoP.

Redundant Residue Number System Assisted Multicarrier Direct-Sequence Code-Division Dynamic Multiple Access for Cognitive Radios

A redundant residue number system (RRNS)-assisted multicarrier direct-sequence code-division dynamic multiple-access (MC/DS-CDDMA) scheme is proposed for application in cognitive radios (CRs). Taking the advantages of both multicarrier direct-sequence code-division multiple access and RRNS, the RRNS MC/DS-CDDMA has a low complexity for implementation and a high flexibility for reconfiguration and is robust to dynamic spectrums. Associated with the RRNS MC/DS-CDDMA, in this paper, the so-called receiver multiuser diversity aided multistage minimum mean-square error multiuser detector (RMD/MS-MMSE MUD) is considered for signal detection. Specifically, three types of RMD/MS-MMSE MUDs are proposed: Type-I.1, Type-II.1, and Type-I.2 RMD/MS-MMSE MUDs. In these MUD schemes, the Type-I.1 MUD carries out the joint detection of all the subcarrier signals using both the observations and the channel state information (CSI) of all the subcarriers. In the Type-I.2 and Type-II.1 RMD/MS-MMSE MUDs, the embedded MMSE-MUDs are implemented subcarrier by subcarrier independently. Furthermore, in the Type-I.2 RMD/MS-MMSE MUD, the autocorrelation matrices used by the MMSE-MUDs are free from CSI. Explicitly, both Type-II.1 and Type-I.2 RMD/MS-MMSE MUDs are suitable for operation in dynamic spectrum environments. Furthermore, our simulation results show that the preceding three types of RMD/MS-MMSE MUDs are capable of making the RRNS MC/DS-CDDMA systems achieve similar error and throughput performance. Owing to the foregoing merits, the RRNS MC/DS-CDDMA employing either Type-I.2 or Type-II.1 RMD/MS-MMSE MUD may be considered one of the highly promising dynamic multiple-access schemes for application in CR systems.

Redundant Residue Number System Based Multicarrier DS-CDMA for Dynamic Multiple-Access in Cognitive Radios

Redundant residue number system (RRNS)-based multicarrier DS-CDMA (MC/DS-CDMA) is proposed for dynamic multiple-access (DMA) in cognitive radios (CRs). The proposed RRNS-based MC/DS-CDMA DMA has the merits of low-complexity for implementation, high-flexibility for reconfiguration and spectrum handoff, robustness to spectrum varying, and fault-tolerance to errors. Specifically, in our RRNS-based MC/DS-CDMA DMA system, RRNS-based orthogonal modulation aided by MC/DS-CDMA is employed for information transmission. At the receiver, signals are detected subcarrier-by-subcarrier independently based on suboptimum MMSE interference cancellation (SMMSE-IC). In performance study, we model the arrival process of primary users (PUs) in primary radios (PRs) as a Poisson process. Both the bit error rate (BER) performance and throughput performance are investigated. Our studies and performance results show that the RRNS-based MC/DS-CDMA constitutes one of the highly promising DMA schemes for application in CRs. It is capable of achieving a substantial throughput with required quality for the CR systems, while without degrading the quality-of-services (QoS) of the PR systems.

Asymptotic Performance Analysis of Time-Frequency-Domain Spread MC DS-CDMA Systems Employing MMSE Multiuser Detection

In this contribution the asymptotic signal-to-interference-plus-noise ratio (SINR) performance of multicarrier direct-sequence code-division multiple-access systems employing time-frequency-domain spreading, i.e., of the TF/MC DS-CDMA systems, is studied, when separate minimum mean-square error multiuser detection (MMSE-MUD) is considered. The separate MMSE-MUD detects signals first in the time (T)-domain and then in the frequency (F)-domain. Based on random matrix theory, closed-form expressions for the asymptotic SINR of the TF/MC DS-CDMA systems using separate MMSE-MUD is derived, when communicating over additive white Gaussian noise (AWGN) channels. The closed-form expressions show that the asymptotic SINR performance is only depended on the T- and F-domain user load factors as well as noise variance. Hence, they are beneficial to evaluation. Furthermore, our simulation and numerical results show that in most cases the asymptotic SINR can provide a good approximation to the SINR achieved by realistic TF/MC DS-CDMA systems employing separate MMSE-MUD.