Mustafa K. Gurcan

Downlink throughput optimization for wideband CDMA systems

This article examines the optimization of throughput in a wireless system. A mathematical model is outlined for a cellular wideband CDMA system. In practical cases, where the maximum transmission power is constrained, power control may not be possible. Self-interference limits the total deliverable rate. It is shown that by optimally allocating bit-rate using a dynamic programming algorithm, a higher bit-rate can be delivered within the same power constraint. Simulation results show on average a 20% increase in total delivered rate can be achieved.

Minimisation of the update response time in a distributed database system

This paper is concerned with the minimisation of the update response time in distributed database systems (DDBS) where resequencing algorithms are used to preserve the consistency of the databases. The authors proposed a novel resequencing technique, in reference [7], namely hop-by-hop resequencing with batch processing for connecting the first stage to the second stage of a two-stage DDBS. In this paper, a stochastic upper bound is calculated for the system response time and it is shown that the system response is smaller than that for a one-stage system of the same size and parameters.

Arrival rate estimation algorithm for single group slotted ALOHA systems

In this letter, a new recursive tracking algorithm is presented that is capable of estimating the real arrival rate, /spl lambda//sub real/, to the system. The estimated value of the arrival rate, /spl lambda//sub estimated/, is used to dynamically adjust the control parameters of the system, hence ensuring that the operating point of the system is pushed toward the required settling point, whatever the real arrival rate to the system. This algorithm utilizes system information through the feedback channel in order to dynamically adjust the estimated value of the arrival rate and hence update the values of the control parameters.

Optimizing radio resource allocation in HSDPA using 2 group allocation

This paper studies an efficient radio resource allocation method for the multicode transmission of High-Speed Downlink Packet Access system. The current HSDPA system allocates equal data rates to multiple channels, causing an inefficient use of radio resources in multipath fading channel. To maximize the system throughput subject to limited radio resources, this paper proposes a computing-efficient 2 group allocation method, which assigns two distinct data rates to 2 groups of channels respectively. The two data rates and the division of the channels can be derived iteratively. The 2 group allocation method significantly outperforms the link adaptation method in the HSDPA system in system throughput, especially when the system operates in high SNR region.

Distributed hand-off schemes for ATM-based beacon type intelligent vehicle communication systems

We propose two distributed hand-off schemes and analyse their performances for future personal communication systems (PCS). The probability of a packet being lost due to a hand-off and that the mean number of packets lost in a hand-off are reduced by more than one to two orders of magnitude depending on the load and the dwell time of the mobile terminal (MT) compared with other distributed hand-off schemes.

Time-efficient resource allocation algorithm over HSDPA in femtocell networks

This paper presents a time-efficient optimal resource allocation algorithm aiming to maximize the system throughput of the single-user High Speed Downlink Packet Access (HSDPA) deployed in a femtocell base station. The system throughput maximization with constrained total power is formulated as a constrained integer programming problem. We first prove that a two-group bit and energy allocation provides the global optimum solution in the system without multipath. We then focus on the use of the two-group allocation method over frequency selective channels. A pre-processing method was used to systematically cluster and remove channels to prevent using energies over severely degraded channels with the two-group allocation approach. This improves the system throughput whilst greatly reducing the computation complexity. The proposed two-group approach with channel removal is suitable for femtocell base station with limited signal processing capability.

An Improved Multicode CDMA Transmission Method for Ad Hoc Networks

A novel two group bit loading algorithm is proposed for use in a multicode CDMA transmission method at the physical layer in order to improve an adhoc radio system performance. The proposed algorithm provides better data rates than rates achievable with the current HSDPA type of algorithm. The paper also proposes a MAC layer enhancement for use in an adhoc network to improve the total throughput by as much as 10 times by increasing the payload duration for the transmission packets. The throughput increases rapidly for a small packet size and reaches an asymptotic value for large packets.

Optimized resource allocation of HSDPA using two group allocation in frequency selective channel

When using an adaptive modulation and coding scheme over multicode CDMA transmission channels, the High Speed Downlink Packet Access (HSDPA) allocates rates equally over parallel channels to provide a wide range of data rates. However, the HSDPA system uses the radio resources inefficiently and suffers from severe performance loss when encountering inter-symbol interference (ISI) over frequency selective channels. This paper proposes a new extended-receiver model and a novel ISI-suppressing linear equalizer for a two group approach whilst nearly doubling the data rate achieved by the HSDPA systems for a given receiver signal-to-noise ratio.

Bit Energy Consumption Minimization for Multi-path Routing in Ad Hoc Networks

A design of an energy-aware disjoint routing discovery scheme as a multi-path routing technique for wireless ad hoc networks is developed. Improvements in the transmission data rates over the links in the routing paths are achieved using a two-group resource allocation scheme to minimize the required amount of energy per bit for each path when the energy per symbol and the packet size are fixed. With a novel load-balancing technique, which evenly loads the energy to each routing path, the information bits can be allocated to the path such that the overall amount of energy consumed per bit is minimized. Two novel multi-path routing techniques are proposed to use the minimized energy consumed per bit in discovering the least-required energy routing paths while reducing the computational complexity.

The Rate Adaptive Throughput Maximization in PAM-Modulated Overloaded System

The current High Speed Downlink Packet Access (HSDPA) system with the Quadrature Amplitude Modulation (QAM) allocates equal data rates to multiple codes for link adaptation which causes large quantization loss in the total data rates. The 2 group allocation method proposed in [1] significantly reduces the quantization loss by optimally adjusting the data rates over each channel for the QAM-modulated underloaded system. This paper applies this rate adaptive throughput maximization problem to the Pulse Amplitude Modulated (PAM) overloaded systems. The proposed system uses complex Grassmannian codes as the spreading sequences and a new complex conjugate concatenation technique for the receiver to further reduce the quantization loss. The numerical results show that the proposed PAM-modulated system employing the 2 group allocation scheme increases the total data rate approximately by 30 - 100% compared with the link adaptation method currently used in the HSDPA system.