Multihop TDD-CDMA cellular system becomes a promising candidate for fourth generation (4G) cellular systems because it provides wider coverage and higher throughput. In this paper, we analyze the uplink system capacity of a multihop TDD-CDMA cellular system. We first analyze a one-hop TDDCDMA cellular system with different base station's (BS's) direct coverage area. We find that the system capacity can be improved if a BS only covers a center small area of the cell. Besides, the high downlink transmission power of the surrounding BSs can degrade the capacity severely. Thus, we propose a multihop TDD-CDMA cellular system to overcome the high downlink inter-cell interference. In our system, a cell area is divided into two regions: inner-region and outer-region. The mobile users in the inner- and outer- region of the cell communicate with BS and relay station (RS), respectively. Based on this model, the uplink system capacity in both regions with the assumption that the inter-cell and intra-cell interference follow the Gaussian distribution is obtained. A comparison equation to provide a fair comparison with conventional one-hop TDD-CDMA cellular system is presented. From the results, we conclude that multihop TDD-CDMA cellular system can improve capacity significantly.

Abstract In this paper, we study the blocking and dropping probability of mobile users in the multi‐service cellular systems with mobile users. Based on the idea that different services may require different signal‐to‐interference ratios and different reuse factors, we proposed a channel allocation scheme calledchannel partitioningto support different services using different reuse factors. Under channel partitioning scheme, the channels in each cell are divided into two or more sets of channels and each set of the channels supports certain service, depending on the required reuse factor of the service. We first apply this channel partitioning with fixed channel allocation scheme called fixed channel partitioning (FCP), where a three‐dimensional Markov chain is developed to analyze the impact of the mobile user. After that a simpler model, which can estimate the numeric result from the closed‐form solution, is presented to make the analysis easier. In order to cater for the traffic variation between services and between cells, a dynamic channel partitioning with flexible channel combination scheme, called FDCP, is proposed to support multiple services. This FDCP tries to minimize the effect of assigned channels on the availability of channels for use in the interfering cells. The analysis and the simulation results show that for equal arrival rate of two services, the proposed FCP and FDCP scheme can provide about 32% and 54% improvement, respectively, in terms of grade of service as compared with conventional FCA scheme using a single reuse factor to support two services for the mobile users. Copyright © 2006 John Wiley & Sons, Ltd.

In UMTS terrestrial radio access (UTRA) standard, each frame consists of 15 TSs for TDD-CDMA system. Any MS can be allocated to any TS for either uplink or downlink transmission. The time slot allocation scheme within these 15 TSs gives the system the freedom of adapting the channel environment. In this paper, we propose and study multihop dynamic time slot allocation schemes, namely dynamic switching point with multihop (DSPM) and maximum interference first (MIF), for TDD-CDMA system. Compared to slot allocation schemes without multihop technique, it is shown that our proposed schemes can improve both the data rate for single user and the overall throughput for the whole system. In addition, we also study the distribution of data transmission speed to demonstrate the effectiveness of each slot allocation scheme clearly.

In this paper, we study the performance of mobile users, in terms of call blocking and dropping probabilities, with our proposed idea of channel partitioning (CP). CP is based on the fact that different services may require different signal-to-interference ratios, and thus different reuse factors. We apply this CP with fixed channel allocation (FCA) scheme called fixed channel partitioning (FCP) in cellular systems. With FCP scheme, each cell is allocated two or more sets of channels. Each set of the channels supports a service in the way that the required reuse factor for that service could be satisfied. A three-dimensional Markov chain is first developed to analyze the impact of the mobile user. Then a simpler model, which can be used to estimate the numeric results from the closed-form solution, is presented to make the analysis easy. Finally, the analytical results are verified with simulation results. The results of this paper show that, for equal voice and data call arrival rate, the proposed FCP scheme can provide about 32% capacity improvement at 1% grade of service (GoS) as compared with FCA scheme. The changing of mobile speed and GoS factor do not affect this improvement. Our proposed FCP scheme could apply in current GSM, GPRS EDGE and future cellular OFDM systems, in which reuse factor plays a very important role.

In this paper, we propose flexible dynamic channel partitioning (FDCP) with a flexible channel-combination scheme to support multiple services. CP is based on the idea that different services may require different signal-to-interference ratios (SIRs), and thus, different reuse factors. In FDCP, different services are allocated to the channels depending on the reuse factors they require. FDCP tries to minimize the effect of the assigned channels on the channel availability to the interfering cells and to reduce the overall reuse distances of the systems.

Due to the limited spectrum in wireless communication cellular systems, channel allocation scheme is a very important issue to achieve high system capacity. In this paper, we present an efficient algorithm using the idea of channel partitioning (CP) to support two types of services requiring different reuse factors. CP is based on the fact that different service requires different SIR and thus can use different reuse factor. A higher SIR required service might use a larger reuse factor while a lower SIR required service might use a smaller reuse factor. We apply this CP algorithm to a previous proposed DCA scheme, DCA-WI. Our newly proposed dynamic channel partitioning with interference information (DCP-WI) tries to manage the channel allocation in a proper way between cells so that each allocation of the channel causes least interference to the neighboring cells. The simulation results show that DCP-WI outperforms FCA and DCA-WI under both uniform and nonuniform traffic distributions.