Saied Abedi

Genetically modified multiuser detection for code division multiple access systems

The problem of multiple access interference (MAI) and intersymbol interference (ISI) suppression in code division multiple access (CDMA) systems is considered. By combining the theory of multiuser detection (MUD) and evolutionary computation, a hybrid genetic engine is proposed, suitable for the detection of CDMA signals in the presence of MAI and ISI. The proposed hybrid detector structure can be extended to most multiuser detectors and used as the base detector within the structure. Using random selection, mutation and crossover operators and a unique chromosome structure, the genetic algorithm evolves the base detector to a group of more efficient detectors in terms of bit-error rate performance. First, a new packet-level genetic MUD technique, using a conventional single user detector as the base detector, is proposed for asynchronous CDMA (ACDMA) with negligible ISI. Then the signal-subspace-based minimum mean square error detector is chosen as a base detector and wrapped inside the hybrid genetic engine to evolve to a better structure nearly to eliminate both ISI and MAI. The novelty of the proposed structure is the way the deterministic closed-form solution of the base detector is mapped to a genetic engine resulting in a group of more efficient and adaptive detectors.

Efficient radio resource management for wireless multimedia communications: a multidimensional QoS-based packet scheduler

Future wireless multimedia systems will support a variety of services with diverse range of capabilities and bit rates. For these systems, it is highly desired for real-time conversational and non-real-time services to efficiently share the available channels and bandwidth in an optimized way. The partitioned resource shaping with either fixed or a slow changing dynamic, proposed for conventional packet scheduling techniques, proves difficult and inefficient under fast-changing dynamics of radio channel and traffic. By taking into account almost all the aspects (dimensions) of quality-of-service (QoS) provisioning, the proposed unified fast dynamic multidimensional QoS-based packet scheduler (MQPS) in this paper elegantly and efficiently encapsulates features of many possible packet scheduling strategies. MQPS applies an optimization and tuning mechanism to packet scheduling weights to adopt the most appropriate packet scheduling and channel assignment strategy in response to the varying traffic and radio channel conditions. As an example, the technique is applied to a high-speed downlink packet access (HSDPA) system. It is shown that MQPS provides significantly better performance than existing techniques by satisfying all the requirements of a successful QoS provisioning to maximum possible level simultaneously.

Synchronization techniques for HIPERLAN/2

HIPERLAN/2 is an orthogonal frequency division multiplexing (OFDM) based wireless LAN standard. The transmission format in HIPERLAN/2 is a burst where the data are always preceded by a preamble. In this paper a reliable synchronization method for a burst data transmission is presented. The algorithm can find the start of the frame and estimate the initial sample of each OFDM symbol. The robustness of the proposed algorithms is checked in adverse conditions of SNP, clipping and multipath.

Reliable Body Area Networks using relays: Restricted Tree Topology

This paper focuses on mechanisms that support the reliable transfer of data for medical applications in wireless Body Area Networks (BANs), in particular for the monitoring by sensors of vital life signs. Recent studies on path-loss models for BANs show that for some scenarios a Star Topology (ST) with a direct, single link, between sensor and coordinator is insufficient. It is thus beneficial to extend the ST to a Tree Topology with a restricted number of hops using relays. In this paper we provide an overview of relevant findings before presenting our Restricted Tree Topology (RTT) design. We then present an experiment that is set up to study the performance of RTT in terms of availability of connectivity, based on Received signal strength at 2.4 GHz using wearable channel sounders with various people sleeping - sleeping has been found to be one of the most difficult scenarios, in terms of reliability, for BAN. Our simulation results show that for certain sleeping positions, RTT improves connectivity by approximately 12% for a receiver sensitivity of -95 dBm. In addition we have shown that without RTT it is not possible to meet the reliability requirement as set out by the IEEE 802.15.6 Task Group for its draft standard.

Hybrid genetic packet scheduling and radio resource management for high speed downlink packet access

Simple wireless scheduling techniques, such as maximum carrier-to-interference ratio (Max. C/I) or round robin (RR), fail to take into account all aspects of quality of service (QoS) provisioning. The fundamentals of evolutionary computation (genetic algorithms) and conventional wireless scheduling techniques are combined and the weaknesses of the existing known techniques are exploited to propose a novel hybrid genetic packet scheduler (HGPS) for high speed downlink packet access (HSDPA). The proposed HGPS outperforms the Max. C/I packet scheduler in terms of total delivered throughput within low delay thresholds.

Improved stability of QoS provisioning for 3G systems and beyond: optimum and automatic strategy selection for packet schedulers

Wireless all-IP multimedia communications systems promise a wide range of services with different quality of service (QoS) requirements and diverse ranges of supported bit rates. This implies that the nature of input traffic load at the base station is expected to vary significantly in time. When radio channels are shared by the existing mixed services (say for example real-time and non-real time services), packet scheduler and channel assignment faces a number of parallel input data pipes which are varied in terms of bit rate. The weights, assigned to different involved aspects in the packet scheduling process, outlines the strategy in terms of importance given to different aspects of packet scheduling. Schedulers with fixed weighting parameters are unable to cope with variable traffic load and radio channel conditions efficiently. The weights assigned to specific traffic or radio channel conditions, might not be suitable for others. In this paper, we propose an optimization and automation algorithm for selection and adaptation of packet scheduling weights. It is shown that the proposed algorithm is capable of improving different aspects involved in a successful QoS provisioning, such as fairness, stability, delivered delay, bit rate and throughput, simultaneously.

A radio aware random iterative scheduling technique for high speed downlink packet access

The overall performance of the high speed downlink packet access (HSDPA) proposal in 3GPP in terms of delay and throughput for various possible radio resource allocation and scheduling algorithms is evaluated using a system level simulator. By exploiting the weaknesses of the conventional wireless scheduling techniques under extreme scenarios, a novel random iterative hybrid scheduling (RIIHS) and radio aware wireless resource allocation technique for HSDPA is introduced. The algorithm has the unique ability of reaching the maximum possible levels of the throughput and fairness and minimum possible level of the delay at the same time.

WINNER Spectrum Sharing with Fixed Satellite Services

The IST 6 framework WINNER project defines spectrum sharing techniques for future wireless communication systems. This paper addresses spectrum sharing capabilities between different radio technologies. More particularly, spectrum sharing between WINNER system and the Fixed Satellite Service (FSS) community is at stake. The goal is to efficiently share the spectrum without causing harmful interference towards the primary system (i.e., FSS). A power assignment mechanism for the coexistence is proposed where different power levels are assigned in the cellular network in the areas surrounding the FSS system. Simulation results for the coexistence between both systems is carried out where the spectrum used by the WINNER system is punctured for the transmission of the primary FSS system. Finally, the results show that spectrum utilization is significantly improved.

Methods for Short Term Spectrum Assignment in Wireless Networks

Proposed technologies in current paper are intended to revolutionize the way in which the radio spectrum is being managed in current wireless networks. The proposed methods as ultimate efficient ways of handling spectrum can be seen as a bridge between current legacy systems (Beyond 3GPP LTE, WiMAX) and future cognitive radio networks. In this paper, we consider the 1ST WINNER European radio network design and outline key additive and complementary technologies to WINNER architecture to achieve further improvements in wireless networks. On a cooperative basis, the proposed technologies open the way for a more flexible exploitation of radio spectrum resources while significantly improving the spectral efficiency and availability. It introduces the novel concepts for short term spectrum assignment in wireless radio networks leading to fast scheduling of spectrum with significant impact on all the relevant radio networks layers. This can be seen even more important than the introduction of fast Base Station (BS) based scheduling in an HSDPA system during late 90s.

Interference Management in Wireless Sensor Networks, Part I: Dynamic Semi-distributed Mechanisms

Interference control and management in wireless sensor networks is a challenging task. Fast and dynamic allocation of wireless sensor communications sub-channels would lead to an efficient exploitation of available capacity and traffic variations. It seems a collective decision in a centralized entity is the best way forward for interference management as the centralized decision making entity which is aware of all the sensor nodes, can avoid the conflicting situation where multiple wireless sensor entities within different cells might show interest in the same radio sub-channel and attempt to occupy it leading to a catastrophic increase of interference within that specific radio sub-channel. In current paper dynamic semi-distributed mechanisms for interference management in wireless sensor networks is proposed to take advantage of both centralized and distributed interference management schemes on a localized basis to improve the QoS in wireless sensor networks.