Farooq Ullah Khan

Design and performance of down link shared control channel for HSDPA

An expanded effort is underway to support the evolution of the UMTS standard to meet the rapidly developing needs associated with wireless Internet applications. The support of high-speed downlink packet access (HSDPA) is provided by means of a new, shared channel called high speed downlink shared channel (HS-DSCH) which is enabled by a number of performance enhancing technologies such as adaptive modulation and coding (AMC), hybrid ARQ (HARQ), fat-pipe scheduling, fast cell site selection (FCSS) and multiple input multiple output (MIMO) antenna techniques. To fully benefit from these technologies, one must guarantee fast and reliable control message exchange between the base station and the user terminals. The downlink signaling is done through the use of shared control channels (SCCH) accompanied with each HS-DSCH. Since the SCCHs, HS-DSCH, and voice channels share the same resources (power, bandwidth), control signalling is often improved at the cost of system resources and capacity. In this paper, we evaluate the performance of the SCCH. The challenges and tradeoffs in the SCCH design will also be discussed.

Priority-based multiple access (PBMA) for statistical multiplexing of multiple services in wireless PCS

A priority based multiple access scheme is proposed to provide multiple services for wireless PCS. The scheme is then applied to the UMTS air interface with emphasis on voice, low delay data, ATM cell relay, and high delay data services. Simulation results are reported to illustrate the performance of the proposed priority-based access scheme in terms of QoS requirements and system capacity.

Performance analysis of link adaptation in wireless personal communication systems

We analyze the link adaptation (LA) performance of a wireless personal communication system supporting two types of voice connections, full-rate and half-rate. Full-rate connections are used when the channel conditions are poor. When the channel conditions are good a full-rate connection is switched to a half-rate for improving spectral efficiency. For analysis simplicity, we consider flat uniform propagation conditions where, for a given propagation exponent, the received powers are determined by distances. Using this propagation model, users in the outer region of the cell will use full-rate channels while users in the proximity of the base station will use half-rate channels. The numerical results are extracted by forming a multi-dimensional Markov chain model of the proposed scheme and are compared with those obtained through a comprehensive computer simulation for call blocking probability, hand-off failure probability and carried traffic. A 42% increase in capacity is achieved when 75% of the users can use halfrate channels.

Link layer buffer size distributions for HTTP and FTP applications in an IS-2000 system

We provide link layer new data and retransmission buffer size distributions for HTTP and FTP applications in an IS-2000 system. The results are given for different TCP window size, TCP segment size, air link FER and data rates. For HTTP application, the number of parallel TCP connections is limited to either 1 or 4. We found that smaller (larger) new data buffers (retransmission buffers) are required at higher data rates. Moreover, for error free transmission over the air link, a large fraction of data (from TCP window) stays in the new data buffers while for the case of link errors, the retransmission buffer size is also large. The maximum retransmission buffer size is a function of the air link RTT (i.e. number of rounds of RLP NAKs) and is independent of the link error rate.

A variable rate channel quality feedback scheme for 3G wireless packet data systems

An expanded effort is underway to support the evolution of the UMTS and cdma2000-1x standards to meet the rapidly developing needs associated with wireless Internet applications. A number of performance enhancing technologies are proposed to ensure high peak and average packet data rates while supporting circuit-switched voice and packet data on the same spectrum. These techniques include adaptive modulation and coding (AMC), hybrid ARQ (H-ARQ) and fat-pipe scheduling. In order to enable these techniques downlink channel quality feedback (CQF) through explicit uplink signaling is necessary. Frequent CQF results in good estimates of downlink channel quality at the base station, which, in turn, improves downlink system performance. However, this comes at the expense of larger uplink signaling overhead, thereby impacting the overall uplink capacity. Infrequent CQF, on the other hand, reduces this signaling overhead in the uplink at the expense of larger errors in the channel quality estimates available at the base station, thereby leading to system performance degradation. In this paper, we present a variable rate CQF scheme that significantly reduces uplink signaling overhead without affecting downlink system performance. In addition to simulation results demonstrating the performance of the proposed scheme, we also compare the reduction in uplink signaling overhead of the said scheme with other known methods.

Performance of PBMA with Contiguous Slot Assignment for Wireless Multimedia Networks

We analyze the performance of Priority-Based Multiple Access (PBMA) with contiguous slot assignment to provide multiple services in wireless PCN environments. The scheme supports data transmission in ATM cell formats to comply with future service provisions in wireless networks. This study extends previous performance analysis conducted for PBMA by considering contiguous slot assignments to offer multiple services. Unlike in previous studies where analytical/numerical and simulation results were provided, the analysis is only achieved through computer simulation because of the state space explosion problem.

Multilevel Channel Assignment (MCA): A Performance Analysis

A channel allocation technique to respect different Carrier to Interference (C/I) ratio constraints in wireless networks supporting multiple services is proposed and analyzed through a system supporting two services, voice and data. Since these services require different Bit Error Rate (BER) performance, different C/I values should be used to meet these requirements. To achieve this goal a cell is divided into concentric zones with the objective of trading off C/I performance of users according to their service class and geographical location. The underlying principle is to offer the minimum required C/I performance for voice users in the inner zone having more than adequate transmission quality in order to improve C/I performance for data users which require very low BER. A Markov chain model of the proposed scheme is identified and results obtained through a comprehensive computer simulation for voice call blocking probability and data access delay are provided.