Bassam M. Hashem

Reverse link capacity and interference statistics of a fixed-step power-controlled DS/CDMA system under slow multipath fading

Power control (PC) on the reverse link of a direct-sequence code-division multiple-access system is essential to increase system capacity. Perfect PC eliminates fluctuations in the received signal level and hence reduces the required signal-to-interference ratio. However, a perfect PC algorithm tracks multipath fading accurately, which results in increasing the intercell interference level. A fixed step PC algorithm becomes almost perfect when the power command rate is too fast compared to the Doppler rate, which is the case for low-mobility users. We investigate the statistics of the intercell interference assuming users are moving slowly. These statistics are then used to find the system capacity. Three parameters that can affect the capacity are considered: the number of the fading process resolvable paths, the maximum transmitted power, and soft handoff.

Future mobile broadband wireless networks: a radio resource management perspective

Summary Future wireless evolution envisages high rates, low hierarchy in the network architecture, antenna array processing, multiple access modes and multihop operation as part of the system concept. To exploit the increased capabilities of the systems in conception, efficient resource management strategies need to be developed. The goal of this paper is to examine the key aspects of the evolution which impact radio resource management for the mobile broadband wireless network, and to emphasize the areas that need to be addressed for servicing mobile users with varying quality of service requirements. Copyright # 2003 John Wiley & Sons, Ltd.

A high-capacity scheduling algorithm for systems employing embedded modulation

The paper proposes a simple scheduling algorithm based on adaptive embedded modulation (EM) for the downlink in urban wireless networks. Embedded modulation allows multiple users to share a single downlink channel simultaneously. The proposed EM scheduling algorithm embeds the user which has the largest carrier-to-interference ratio (C/I) with each of the lower C/I users in turn. Simulation results show that the EM scheduler, employing adaptive coded modulation, can improve the average throughput of a given downlink by up to 33% over a round robin scheduler, while still maintaining acceptable fairness amongst the system users.

Radio Resource Management for Wireless Internet

It is anticipated that there will be a strong market for a rich variety of wireless internet-based multimedia devices in the not-too-distant future. It is quite difficult to predict the nature of these devices as well as the corresponding applications; but it is certain that those devices and applications will have very different QoS, rate, delay and power constraints. Arguably, effective management of radio resources (through techniques such as interference management and cancellation, dynamic resource allocation and control, packet scheduling and call admission control) is not only essential in future networks, but is also the key factor in the efficient and affordable deployment and operation of these networks. Proportional to its importance, radio resource management appears to be an immensely complex task as well in future wireless networks. However, it is not yet clear whether this task is inherently difficult or whether it only appears so due to our lack of sufficient understanding of this multidimensional problem. As deeper insight into this field is developed by researchers, it is foreseeable that very efficient and straightforward (although suboptimal) algorithms can be developed. Research activities towards 4th generation mobile communication networks have already started; in the meanwhile, the standards for the 3rd generation networks are continuously being revised for higher performance. Not surprisingly, one main area of focus in all these activities is the better management of radio resources. This Special Issue is composed of nine papers (the first three of which are invited papers from the industry) discussing various aspects of radio resource management within the framework of wireless internet. The first invited paper, authored by Shalini Periyalwar et al. (Nortel Networks, Canada), is a visionary one in which radio resource management related issues are discussed for the envisioned future mobile broadband wireless networks. In the second invited paper, Werner Mohr (Siemens, Germany) presents an analytical model for estimating the spectrum demand for beyond-3G mobile networks, based on projected data rate requirements. In the third and final invited paper, Ralph Gholmieh (Ericsson, USA) and Farideh Khaleghi discuss one important feature in the recently revised version of the IS-2000 standard, the control-hold mode, which aims to maximize the throughput in the forward link. In the paper entitled ‘Linear successive interference cancellation in DS-CDMA systems’, Fredrik Berggren and S. Ben Slimane analyze the capacity performance of a receiver with interference cancellation capability which is supported by a novel interference cancellation-aware power control algorithm. The following two papers discuss different aspects of scheduling in CDMA networks. The first paper, authored by Sonia Aissa, Amine Maaref and Paul Mermelstein, proposes a novel flow control algorithm for multi-rate networks with interference cancellation, while the second paper authored by Tao Shu and Zhisheng Niu, demonstrates the optimum method of choosing (with respect to throughput maximization) concurrently transmitting data users. The paper authored by Walid Ibrahim, John W. Chinneck and Shalini Periyalwar, proposes a novel QoS-based charging and resource allocation framework which may potentially allow the network operators to pursue a wide variety of policy options. In the paper entitled ‘Radio resource management techniques for UE-MAC in 3GPP W-CDMA systems’, Sheng-Tzong Cheng and Jian-Liang Lin investigate the adverse effects of rapid transmission rate changes on the BER and they

A new algorithm to reduce the deviation in the base stations transmitted powers during soft handoff in CDMA cellular systems

Soft handoff (SHO) is one of the critical components that determine the performance of a CDMA cellular system. The mobile station in 3G systems send power control commands to the base stations to adjust their powers. These power control commands can be received in error by on of the base stations in the active set serving the mobile. This results in the base stations transmitted powers deviating. Reducing the deviation in the base stations transmitted powers helps to achieve the desired diversity gain from SHO. We propose to change the way the base stations respond to power control commands. This does not require changing the way the mobile issues the power control commands. From the simulation results we see that at a speed of 5 km/h, the probability that the difference in the two base stations transmitted powers being greater than 5 dB is about 25% using the conventional scheme while it is only 8% for the proposed scheme (majority voting over two commands). We notice also that the base stations average transmitted power is reduced by employing the majority voting scheme.