Throughput analysis of IEEE 802.11e EDCA under heterogeneous traffic

The amended version of IEEE 802.11e defines the enhanced distributed channel access (EDCA) for quality of service (QoS) connections. EDCA provides a priority scheme to classify different traffic categories by the arbitration inter-frame space (AIFS), and the initial and maximum contention window sizes. Most previous Markov chain analyses of EDCA have concentrated on the effect of contention window size, they neglected the effect of AIFS. In this paper, we consider of AIFS events among each back-off procedure and evaluate the saturation throughput of the IEEE 802.11e EDCA under heterogeneous traffic scenarios. The analytical model is based on the differentiated AIFS and uses the discrete time slot to analyses the external collision time. We take advantage of extensive simulation studies to validate the accuracy of the proposed model. Our models accurately estimate the effects of varied back-off window size and AIFS under heterogeneous traffic.     

Multi-Channel Assignment Schemes and Handoff Study in CDMA Cellular Systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multi-channels for a CDMA system is requisite for satisfying the demand of capacity. In this paper, three schemes of multi-channel assignment are proposed. Based on computer simulation, performance measures, e.g. blocking probabilities, the overall capacity, the capacity of each channel, and the number of re-accesses, are obtained. Since the same frequency channel may be assigned to two adjacent cells, the effect of soft handoff is also considered. Numerical results demonstrate that scheme 3 (i.e., the random re-selection scheme) performs the best of the proposed three schemes because it provides the highest system capacity while keeping the cost of accessing channels (i.e., in terms of number of channel accesses) to a minimum.     

Performance Analysis of QoS-Based Voice/Data CDMA Systems

This paper examines the performance of a quality-based voice/data CDMA systemwhere new and handoff calls are considered. A call request for handoff dataqueues up if the signal-to-interference ratio exceeds a predefined thresholdwhile priority is given to handoff voice calls by exclusively reserving somechannels for them. The transmission rate of data users may vary according tomeasured SIR value. The transmission power of voice and data users may bedifferent. Important performance measures of the system such as blockingprobability and system capacity for voice and data calls are also compared fordifferent schemes.     

Hot-spot traffic relief with a tilted antenna in CDMA cellularnetworks

Direct-sequence code division multiple-access (DS-CDMA) cellular networks are highly promising in terms of their potential to provide more capacity than an advanced mobile phone system (AMPS). However, heterogeneous traffic loading causes traffic congestion in a CDMA hot-spot. This paper presents a tilted antenna mechanism for sectored cells in CDMA cellular networks to relieve the congestion in a hot-spot sector. The fixed antenna-tilted mechanism, which only tilts the hot-spot antenna, can provide the merit of traffic balancing. Besides, we design a dynamic antenna-tilted mechanism in which tilting the antennas of the hot spot and its adjacent cell sectors is based on varying the signal-to-noise ratio (SNR). The dynamic mechanism can automatically tilt the antenna corresponding to the variation of traffic. Consequently, more capacity can be provided than in a fixed tilting mechanism, which only tilts the hot-spot antenna. Another benefit is the traffic-balancing effect with a tilted-antenna mechanism that reduces the transceivers of a hot-spot base station. Therefore, extra facilities are unnecessary for the hot spot than for a normal or light traffic sector     

Performance Study for Two-Tier CDMA Cellular Systems with Multi-Channel Access

The CDMA cellular system can provide more capacity than AMPS systems and the hierarchical layer of cells is required for system design. However, system performance and capacity is degraded due to the cochannel interference between microcell and macrocell if a single frequency channel is shared. This paper proposes three multi-channel access schemes where various frequency channels are assigned for microcell and macrocell. Performances of channel capacity, blocking probability and blocking ratio in uplink and downlink are evaluated. Due to channel segregation and thus the cochannel interference among macrocell and microcell are minimized, the proposed scheme 3 where all channels are accessible sequentially in macrocell and microcell performs the best in system capacity and blocking probability than the other schemes.     

Performance evaluation for multichannel access schemes in CDMA cellular systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multichannels for a CDMA system is a requisite to satisfy the demanded capacity. In this paper, five schemes of multichannel assignment are proposed. Based on computer simulation, performance measures such as blocking probabilities, the overall capacity, the capacity of each channel and the number of retrials are obtained. Simulation results indicate that the SIR-based selection scheme is preferable to the other schemes. © 1998 John Wiley & Sons, Ltd.     

Performance study for a microcell hot spot embedded in CDMAmacrocell systems

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. We investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. A downlink power control scheme and two power control methods for the uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for a microcell are also noted, such as more power need to be transmitted by a microcell base station (BS) if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by the uplink and downlink, respectively. With downlink power control, the microcellular capacity can be increased. However, the combination of downlink power control for the microcell and C/I uplink power control for the macrocell causes the overall system capacity to significantly increase     

A Fast IMS Service Recovery Mechanism for the Handover Over MIH-Capable Heterogeneous Networks

IP multimedia subsystem (IMS) is the core multimedia network in the next generation all-IP environment. It provides access independence for multimedia applications across fixed and mobile access networks. When a roaming IMS subscriber connects to IMS through mobile access networks, handover becomes a critical issue; this needs to be addressed. Since IMS concerns application layer handover for session mobility, the application layer handover takes a long time for recovering the suspended sessions according to the standard IMS session reestablishment procedure. This introduces noticeable service interruption to end users and cannot be tolerated for real-time applications. In this paper we propose a fast IMS service recovery mechanism to shorten the service recovery latency by combining the IEEE 802.21 Media Independent Handover service and the IRTF Media-Independent Pre-Authentication frameworks. The proposed mechanism performs the necessary IMS registration and QoS re-negotiation procedures in advance of lower-layer handover. Thus it reduces the service recovery latency for suspended services. With parallel design in time, the proposed mechanism is able to shorten overall handover relevant latency as well. Technical examination shows that it is easy to deploy the proposed mechanism in current multimedia service environments.     

A Novel Bandwidth Allocation Algorithm for IEEE 802.16 TDD Mode Wireless Access Networks

In this paper, we propose a novel bandwidth allocation algorithm for a two-tier hierarchy in IEEE 802.16 time division duplex mode wireless access networks under symmetric and/or asymmetric uplink and downlink traffic input. We demonstrate the performance of the new bandwidth allocation algorithm in terms of accumulated throughput (cumulative bandwidth) and fairness in both infinite and finite buffer cases compared with others by simulations. The simulation results show that the proposed algorithm not only can provide much better fairness and maintain satisfactory QoS support and high cumulative bandwidth but also in the case of finite buffer depth is less buffer-consuming than the others, meaning that the hardware cost can be reduced by employing the proposed algorithm.