In virtual cellular network (VCN), proposed for high-speed packet mobile communications, the signal transmitted from a mobile terminal is received by wireless ports distributed in each virtual cell and relayed to the central port that acts as a gateway to the core network. In this letter, we apply the multi-hop maximal ratio combining (MHMRC) diversity and propose the route modification algorithm in order to improve transmit power efficiency degradation caused by the carrier frequency difference between the control and the data communication channels for VCN. The transmit power efficiency and the distribution of the number of hops are evaluated by computer simulation for a VCN.

In this paper, we study a delay transmit diversity system combined with antenna diversity reception that transmits the time-delayed and weighted versions of the same signal from multiple antennas. At a receiver, multiple receive antennas are used and all delayed signals received on multiple antennas are coherently combined by a Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) after Rake combining is theoretically analyzed to show that the optimum solution is to transmit only from the best antenna that has the maximum equivalent channel gain seen after Rake combining. The bit error rate (BER) performance is theoretically analyzed and evaluated by computer simulation. The combined effect of transmit diversity and transmit power control (TPC) is also investigated.

In this paper, expressions are derived for the bit error rate (BER) of the multicarrier-CDMA (MC-CDMA) downlink in the presence of pure impulsive interference and a frequency-selective fading and the BER performance is numerically evaluated by a Monte-Carlo simulation method. Minimum mean square error combining (MMSEC) and orthogonal restoration combining (ORC) are considered for frequency-domain equalization. The joint weight of antenna diversity reception using maximal ratio combining (MRC) and frequency equalization combining is derived. The MC-CDMA transmission performance in the presence of pure impulsive interference is compared with that of DS-CDMA transmission.

Independent shadowing losses are often assumed for computing the frequency reuse distance of cellular mobile communication systems. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and interfering signals. We investigate, by computer simulation, how the shadowing correlation impacts the frequency reuse distance of a power controlled cellular system. It is pointed out that the shadowing correlation impacts the frequency reuse distance differently for the uplink and downlink.

Without transmit power control (TPC) and Rake combining, the uplink capacity of a direct sequence code division multiple access (DS-CDMA) packet mobile communication system significantly degrades due to the near-far problem and multipath fading. In this letter, assuming a single cell system with an interference-limited channel, the impact of the joint use of Rake combining and TPC on the uplink capacity is evaluated by computer simulation. Slow TPC is found to give a link capacity larger than fast TPC. This is because, with slow TPC, the received signal power variations due to fading remain intact and this results in a larger capture effect.

A random transmit power control (TPC) is applied to DS-CDMA/TDD packet mobile radio, which controls the transmit power so as to intentionally vary the received signal power in order to obtain the large capture effect. The uplink capacity with the random TPC in a frequency-selective fading channel is evaluated by computer simulation. The simulation results show that the random TPC provides larger link capacity than slow TPC.

Four imperfections encountered in transmitter power control (TPC) for direct sequence code division multiple access (DS/CDMA) cellular mobile communications systems, faulty TPC, finite dynamic range, restricted site diversity, and non-uniform user distribution, are investigated where account is taken of the effect of the propagation constant on the traffic capacity. Computer simulation schemes for traffic capacity estimation under these TPC imperfections are presented. Traffic capacity estimates are produced for a representative DS/CDMA cellular mobile communications system.

Recently, major services provided by mobile communications systems are shifting from voice conversations to data communications over the Internet. There is a strong demand for increasing the data transmission rate. However, an important problem arises; larger peak transmit power is required as transmission rate becomes higher. In this paper, we propose a wireless multi-hop virtual cellular concept to avoid this power problem. The virtual cellular network consists of a central port, which is a gateway to the network, and many distributed wireless ports. Transmit power and frequency efficiencies of the virtual cellular network are evaluated by computer simulation to compare with that of the present cellular networks. In the wireless multi-hop virtual cellular network, routing among wireless ports is an important technical issue. We propose a routing algorithm based on the total uplink transmit power minimization criterion and evaluate the total transmit power by computer simulation.

In this paper, we study DS-CDMA delay transmit diversity that transmits the weighted and time-delayed versions of the same signal from multiple antennas in a frequency non-selective fading environment. At a receiver, one receive antenna is used and the received delayed signals are coherently combined by Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) is theoretically derived to reveal that the optimum solution is to transmit only from the best antenna that has the maximum channel gain. The bit error rate (BER) performance improvement over conventional delay transmit diversity is theoretically analyzed and confirmed by computer simulations. The combined effect of transmit diversity and transmit power control (TPC) is also evaluated. Furthermore, the impact of fading decorrelation between the transmit and receive channels is also investigated for both the time division duplex (TDD) and frequency division duplex (FDD) schemes.

In this paper, we propose a novel scheme of cooperative relaying network based on data exchange between relays before forwarding their received data to destination. This inter-relay data exchange step is done during an additional middle-slot in order to enhance the transmit signals from relays to the destination under low transmit power condition. To reduce the propagation errors between relays as well as the required transmit power during this data exchange, only the relay possessing the highest SNR is engaged into exchanging data by forwarding its received signal to the other relays. As for the remaining non-selected relays, i.e. with low SNR, the transmitted signal is estimated by using both signals received separately at different time slots (i.e., 1st and 2nd slot) from source and the 'best' selected relay, respectively, emulating virtual antenna array where appropriate weights for the antenna array are developed. In addition, we investigate distributed transmit beamforming and maximum ratio combining at the relays and the destination, respectively, to combine coherently the received signals. At the relay optimal location and for low SNR condition, the proposed method has significant better outage behavior and average throughput than conventional methods using one or two time slots for transmission.

User capacity of a DS/CDMA cellular mobile radio system employing transmitter power control (TPC) is investigated. Assuming log-normally distributed control error, outage probability is evaluated through computer simulations. The user capacity is dramatically decreased as the power control error increases. If the standard deviation is larger than about 2dB, the user capacity is decreased by more than 60%. It is shown that power control error with a standard deviation of less than or equal to 0.5dB is required to accommodate 90% of the maximum user capacity. The capacity decrease in the reverse and forward link channels due to non-uniform user distributions are also investigated. It is shown that if system users are densely distributed within the zone fringe whose thickness is 80% of the radius, the reverse link capacity is decreased by about 22%. The forward link capacity is comparatively insenstitive to non-uniform user distribution.

In DS-CDMA cellular communications systems, the single frequency reuse can be utilized. Since large other-cell interference is produced, the well known soft handover or site diversity must be used. If the single frequency reuse is not utilized to avoid the other-cell interference, we will face the frequency allocation problem, similar to FDMA systems. In this paper, a DS-CDMA cellular system using band division is proposed. The available wide frequency band is divided into several narrow frequency bands and the different frequency bands are allocated to adjacent cells so as to avoid the large other-cell interference. For the frequency allocation, the channel segregation distributed channel allocation (CS-DCA) algorithm is applied. The link capacity is evaluated by computer simulation.

Adaptive antenna array is a promising technique to increase the link capacity in mobile radio communications systems by suppressing multiple access interference (MAI). In the mobile radio, the received signal consists of discrete paths, each being a cluster of many irresolvable paths arriving from different directions. For large arrival angle spread of each cluster of irresolvable paths, antenna array cannot form a beam pattern that sufficiently suppresses MAI even in the presence of single interference signal and hence, the transmission performance may degrade. In this situation, the use of antenna diversity may be a better solution. It is an interesting question as to which can achieve a better performance, antenna diversity reception or adaptive antenna array. In this letter, we study the impact of the arrival angle spread on the DS-CDMA transmission performances achievable with adaptive antenna array and antenna diversity reception. It is pointed out that the arrival angle spread is an important parameter to determine the performances of adaptive antenna array and antenna diversity.

Multi-hop networks have been proposed to increase the data transmission rate in wireless mobile networks, and consequently improve the quality of experience of cell-edge users. A successive resource allocation scheme (SAS) has been proposed for a 2-hop virtual cellular network (VCN). In a multi-cell environment, the performance of SAS degrades because of intra-cell and inter-cell interference. In order to alleviate the effect of intra-cell and inter-cell interference and consequently increase the channel capacity of the VCN, this paper proposes the sequential iterative allocation scheme (SIS). Computer simulation results show that, compared to SAS, SIS can improve the fairness, the ergodic, and the outage channel capacity per mobile terminal (MT) of the VCN in a multi-cell environment. This paper also analyzes the performance of the VCN compared to that of the single hop network (SHN) when SIS is applied in a multi-cell environment. Using SIS, VCN can provide higher ergodic channel capacity, and better degree of fairness than SHN in a multi-cell environment. The effect of the number of wireless ports (WPs) in the VCN is also investigated, and the results suggest that adding more WPs per virtual cell in the VCN can enhance the outage channel capacity per MT and the degree of fairness of the VCN.

In the next generation mobile network, the demand for high data rate transmission will require an increase in the transmission power if the current mobile cellular network architecture is used. Multihop networks are considered to be a key solution to this problem. However, a new resource allocation algorithm is also required for the new network architecture. In this paper, we propose a resource allocation scheme for a parallel relay 2-hop OFDMA virtual cellular network (VCN) which can be applied in a multiuser environment. We evaluate, by computer simulation, the ergodic channel capacity of the VCN using the proposed algorithm, and compare the results with those of the conventional single hop network (SHN). In addition, we analyze the effect of the location of the relay wireless ports on the ergodic channel capacity of the VCN. We also study the degree of fairness of the VCN, using the proposed scheme, compared with that of the SHN. For low transmission power, the simulation results show: a) the VCN can provide a better ergodic channel capacity and a better degree of fairness than the SHN, b) the distance ratio for which the ergodic channel capacity of the VCN is maximal can be found in the interval 0.20.3, c) the ergodic channel capacity of the VCN remains better than that of the SHN as the number of users increases, and d) as the distance between the relay WPs and the base station increases, the channel capacity of VCN approaches that of the SHN.

Direct sequence code division multiple access (DS-CDMA) is attractive for mobile radio use because of its inherently high capacity. There is great demand for mobile radio to offer multimedia services. This means that various service rates and qualities should be supported. DS-CDMA systems are flexible and can accommodate various user rates easily so these demands can be met. As many users will occupy the same frequency band simultaneously, the traffic capacity of a DS-CDMA system is determined by interference power. Interference cancellation is one of the important techniques in decreasing interference power at the demodulation stage and thus increasing traffic capacity. In this paper, we propose the delayed symbol combining interference canceller which can suppress the interference from various users sending at different information rates. Performance of the proposed method is calculated by computer simulations. Furthermore, the effect of adding forward error correction to the proposed canceller is also evaluated by computer simulations. In the quasi static flat fading environment, it is found that the Eb/No degradation due to interference is suppressed to 3 dB at BER=10-3 with 24 users. In the quasi static frequency selective fading environment, it is found that the required Eb/No of the frequency selective fading canceller is about 11 dB better than that of the flat fading canceller for the target BER of 10-3. It is found that BER<10-3 is achieved with forward error correction and bit interleaving even when the maximum Doppler frequency normalized by low data bit rate is 0. 0008 and Eb/No is 20 [dB] in frequency selective fading and 30 [dB] in flat fading.

In the literature, many resource allocation schemes have been proposed for multi-hop networks. However, the analyses provided focus mainly on the single cell case. Inter-cell interference severely degrades the performance of a wireless mobile network. Therefore, incorporating the analysis of inter-cell interference into the study of a scheme is required to more fully understand the performance of that scheme. The authors of this paper have proposed a parallel relaying scheme for a 2-hop OFDMA virtual cellular network (VCN). The purpose of this paper is to study a new version of that scheme which considers a multi-cell environment and evaluate the performance of the VCN. The ergodic channel capacity and outage capacity of the VCN in the presence of inter-cell interference are evaluated, and the results are compared to those of the single hop network (SHN). Furthermore, the effect of the location and number of wireless ports in the VCN on the channel capacity of the VCN is investigated, and the degree of fairness of the VCN relative to that of the SHN is compared. Using computer simulations, it is found that in the presence of inter-cell interference, a) the VCN outperforms the SHN even in the interference dominant transmission power region (when a single cell is considered, the VCN is better than the SHN only in the noise dominant transmission power region), b) the channel capacity of the VCN remains greater than that of the SHN even if the VCN is fully loaded, c) an optimal distance ratio for the location of the wireless ports can be found in the interval 0.2∼0.4, d) increasing the number of wireless ports from 3 to 6 can increase the channel capacity of the VCN, and e) the VCN can achieve better outage capacity than the SHN.

In this paper, the channel segregation dynamic channel allocation (CS-DCA) scheme is applied to a multi-hop DS-CDMA virtual cellular network (VCN). After all multi-hop routes are constructed over distributed wireless ports in a virtual cell, the CS-DCA is carried out to allocate the channels to multi-hop up and down links. Each wireless port is equipped with a channel priority table. The transmit wireless port of each link initiates the CS-DCA procedure and selects a channel among available ones using its channel priority table to check. In this paper, the channel allocation failure rate is evaluated by computer simulation. It is shown that CS-DCA reduces remarkably the failure rate compared to FCA. The impact of propagation parameters on the failure rate is discussed.

In mobile communication systems, high speed packet data services are demanded. In the high speed data transmission, throughput degrades severely due to severe inter-path interference (IPI). Recently, we proposed a random transmit power control (TPC) to increase the uplink throughput of DS-CDMA packet mobile communications. In this paper, we apply IPI cancellation in addition to the random TPC. We derive the numerical expression of the received signal-to-interference plus noise power ratio (SINR) and introduce IPI cancellation factor. We also derive the numerical expression of system throughput when IPI is cancelled ideally to compare with the Monte Carlo numerically evaluated system throughput. Then we evaluate, by Monte-Carlo numerical computation method, the combined effect of random TPC and IPI cancellation on the uplink throughput of DS-CDMA packet mobile communications.

Two error control schemes for Transmission Control Protocol (TCP) connection on a wireless network are proposed that can minimize the degradation in radio link throughput due to retransmission. One scheme is based on the discard of TCP retransmission packets, and the other is based on the suppression of transmission delay fluctuation. Simulation results show that the degradation in throughput is reduced by 7.2% by using each proposal scheme when the frame error rate is 10e-3.