In the pursuit of ever increasing demand of higher data rates, modern wireless communication systems are resorting to tighter frequency reuse patterns thereby leading to interference-limited systems. Recently proposed interference-aware receiver [1] is a low complexity and efficient receiver design for interference mitigation in cellular systems. However this advanced receiver necessitates the channel knowledge of both the desired and interfering signals which may not be available in a practical system. In this paper, we investigate the performance of interference-aware receiver under imperfect channel state information (CSI). We consider uncorrelated Rayleigh flat fading channels and model the estimation error as independent complex Gaussian random variables. We derive upper bound on the pair wise error probability (PEP) and show that the interference-aware receiver is characterized by full diversity in the presence of channel estimation errors. We compare the performance of interference-aware receiver with that of MMSE receiver and show that the degradation in the performance of MMSE receiver is much more pronounced than that of interference-aware receiver under imperfect CSI.

Femtocell networks are widely being deployed to extend cellular network coverage in indoor environments such as office building spaces and homes. In order to mitigate possible co-channel interferences, designs based on the concept of cognitive radio (CR) that enables an overlay between macrocell (primary) and femtocells (secondary) has been considered a promising approach. The paper first introduces a general dynamic sensing mechanism, which is characterized by performing per-time-slot fast sensing upon a channel at the femto devices, in contrast to the conventional CR design that each channel is sensed for identifying available TV bands. Then, based on the proposed sensing mechanism, the paper analyzes the possible throughput achieved by a femto user via a Markov chain model. Numerical experiment is conducted to verify the proposed model and examine different sensing scenarios using the practical GSM standard parameters, and prove the effectiveness of the proposed approach.

In enhanced distributed channel access (EDCA) protocol, small contention window (CW) sizes are used for frequent channel access by high-priority traffic (such as voice). But these small CW sizes, which may be suboptimal for a given network scenario, can introduce more packet collisions, and thereby, reduce overall throughput. This paper proposes enhanced collision avoidance (ECA) scheme for AC_VO access category queues present in EDCA protocol. The proposed ECA scheme alleviates intensive collisions between AC_VO queues to improve voice throughput under the same suboptimal yet necessary (small size) CW restrictions. The proposed ECA scheme is studied in detail using Markov chain numerical analysis and simulations carried out in NS-2 network simulator. The performance of ECA scheme is compared with original (legacy) EDCA protocol in both voice and multimedia scenarios. Also mixed scenarios containing legacy EDCA and ECA stations are presented to study their coexistence. Comparisons reveal that ECA scheme improves voice throughput performance without seriously degrading the throughput of other traffic types.

Abstract Distributed coordination function (DCF) is the basis protocol for IEEE 802.11 standard wireless local area networks. It is based on carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. DCF uses backoff process to avoid collisions on the wireless channel. The main drawback with this process is that packets have to spend time in the backoff process which is an additional overhead in their transmission time. The channel is rendered idle when all the stations defer their transmissions due to their backoff process. Therefore, the channel utilization and the total throughput on the channel can be improved by reducing the average time spent by the packets in the backoff process. In this paper, we propose a new media access coordination function called proposed media access protocol (PMAP) that will improve the channel utilization for successful packet transmission and therefore, the total achievable throughput. In addition, we propose an analytical model for PMAP under saturated conditions. We use this model to analyze the performance of PMAP under saturated conditions. To substantiate the effectiveness of our model, we have verified the model by simulating PMAP in NS‐2. Simulation and analytical results show that under saturated conditions, PMAP shows profound improvement in the throughput performance compared to DCF. In addition, the throughput performance of PMAP under unsaturated conditions is presented. We have also presented the delay performance of PMAP and DCF through simulation in both saturated and unsaturated conditions. Simulation results show that the average delay experienced by the packets is less in PMAP compared to DCF. Further, the variance in the packet delay is same for both PMAP and DCF protocols under unsaturated conditions. From the performance results obtained for PMAP under both saturated and unsaturated conditions, it can be concluded that PMAP is superior in performance compared to DCF. Copyright © 2006 John Wiley & Sons, Ltd.

Enhanced distributed channel access (EDCA) is the basis protocol in IEEE 802.11e protocol suite. It is used for providing differentiated quality of service (QoS) in IEEE 802.11e standard wireless local area networks (WLANs). One of the main drawbacks in EDCA is the small values used for minimum and maximum contention window (CW) sizes for the AC_VO access category, the queue designated for voice transmission. The AC_VO queues of the QSTAs are very aggressive in transmitting their packets on to the channel due to their small CW sizes. This leads to degradation in the actual voice throughput performance even when the network size is small. This work proposes a new modification to the collision avoidance mechanism used by AC_VO queues without seriously effecting the performance of other traffic categories such as video and data. Extensive simulations are carried out to verify the performance of the proposed enhancement to the original collision avoidance mechanism.

This paper proposes a new distributed media access control (MAC) scheme to improve the network performance of Multiple-Input Multiple-Output (MIMO) wireless systems. In particular, this novel MAC scheme efficiently schedules two simultaneous transmissions between wireless stations (each equipped with three antennas) that are located in a single collision domain. Along with weighted nulling and intelligent packet fragmentation, this MAC scheme is capable of providing more efficient utilization of channel resources. The proposed MIMO-aware MAC scheme is compatible with the IEEE 802.11 standard. Detailed simulations are carried out to study the performance of the proposed scheme. The performance of the MIMO-aware MAC scheme is also compared with a recently proposed MIMO MAC scheme in the literature which is compatible with the IEEE 802.11 standard. Comparisons reveal that the proposed MIMO-aware MAC scheme achieves better throughput and delay performance under both saturated and unsaturated conditions.

The IEEE 802.16 WirelessMAN standard provides a comprehensive quality-of-service (QoS) control structure to enable flow Isolation and service differentiation over the common wireless network Interface. By specifying a particular set of service parameters, the media access control (MAC) mechanisms defined in the standard are capable of offering service guarantees on the connection basis. However, the design of efficient, flexible and yet bandwidth-saving scheduling algorithms for such QoS provisioning still remains an open topic. This paper proposes a new distributed QoS control scheme that guarantees particular service parameter settings for both uplink and downlink connections. Detailed simulation experiments are presented to study the performance and to validate the effectiveness of the proposed algorithm.

Many modifications have been proposed in the literature to improve the performance of distributed coordination function (DCF) under congested environments. These improvements are achieved by modifying the contention window reset mechanism used in DCF protocol. However the main drawback with these modifications is the high backoff process overhead. Therefore we recently proposed a new DCF (N-DCF) protocol to reduce backoff process overhead. In this paper, we proposed a throughput model for N-DCF which is applicable for any arbitrary load conditions. The model was verified using NS- 2 simulations. We then compared the performance of N-DCF with the other recently proposed modifications to DCF in the literature. Comparisons have revealed that only N-DCF provides improvement in throughput performance under RTS/CTS access mechanism. Based on our observations, we further proposed two more media access control protocols to improve the performance of DCF protocol in both basic and RTS/CTS access mechanisms. Finally, we compared the performance of our proposed protocols with our original N-DCF protocol.