Wideband wireless access based on DS-CDMA (W-CDMA) is a promising access technique for the 3rd generation mobile communication systems using 2 GHz carrier frequencies. In this paper, several promising techniques to enhance significantly the link performance or capacity are identified. They are (a) interference reduction techniques: interference cancellation and adaptive antenna array (b) required E b/I0 reduction techniques: channel coding and adaptive transmit power control (TPC). For the last decade, many theoretical studies have been done on interference cancellation and adaptive antenna array techniques. Now, it is time to implement real hardware to demonstrate their capabilities under real mobile radio propagation channels. In mobile radio, because of the well-known near/far problem and the adverse effect of fading, fast TPC is indispensable. Currently, a simple closed-loop fast TPC is adopted. The use of a more sophisticated adaptive fast TPC algorithm, which can adapt its power up/down step size according to the variations in channel conditions, may reduce the power control error, resulting in reduced interference to other users. Fast TPC and channel coding work complementarily against fading. Channel coding is another interesting area of research. Turbo coding is the most promising technique. In this paper, the above mentioned techniques are introduced. Preliminary experimental results of interference cancellation and adaptive antenna array techniques are also presented.

Spatial despreading weight based on minimum mean square error (MMSE) criterion is derived for orthogonal space-time spreading transmit diversity (OSTSTD) in a fast fading channel, taking into account the inter-antenna interference (IAI) and the inter-code interference (ICI) caused by orthogonality distortion of time-domain spreading codes. Average bit error rate (BER) performance is theoretically analyzed and confirmed by computer simulation to show that the diversity gain can be obtained even in a fast fading.

In this paper, iterative adaptive soft parallel interference canceller (ASPIC) is proposed for turbo coded multiple-input multiple-output (MIMO) multiplexing. ASPIC is applied to transform a MIMO channel into single-input multiple-output (SIMO) channels for maximum ratio diversity combining (MRC). In the ASPIC, replicas of the interference are generated and subtracted from the received signals. For the generation of replicas with higher reliability, iterative ASPIC is proposed. It performs the iterative interference cancellation by feedback of the log-likelihood ratio (LLR) sequence obtained as the turbo decoder output. For iterative ASPIC, at the transmitter, the information sequence and parity sequence are transmitted from different antennas. In this paper, the achievable bit error rate (BER) performance, in a Rayleigh fading channel, for the turbo coded MIMO multiplexing with the proposed iterative ASPIC system is evaluated by computer simulation.

In the next generation mobile communication systems, multiple-input multiple-output (MIMO) multiplexing is an indispensable technique to achieve very high-speed data transmission with a limited bandwidth. In MIMO multiplexing, it is necessary to estimate the channels between transmit and receive antennas for signal detection. In this paper, we propose a minimum mean square error (MMSE) channel estimation using cyclic delay pilot for single-carrier (SC)-MIMO multiplexing. In the proposed channel estimation, the same pilot block is altered through the addition of different cyclic delays and transmitted from different antennas at the same time for simultaneous estimation of all channels between transmit and receive antennas. We evaluate by computer simulation the bit error rate (BER) performance of MIMO multiplexing using the proposed channel estimation and compare it to those using time-multiplexed pilot based channel estimation (TMP-CE) and code-multiplexed pilot based channel estimation (CMP-CE).

In downlink MC-CDMA, orthogonal variable spreading factor (OVSF) codes can be used to allow multirate communications while maintaining the orthogonality among the users with different data rates. In this paper, we point out that simple selection of the OVSF codes results in degraded performance. We show that this happens because simple code selection results in power concentration over certain consecutive subcarriers; severe power loss in the received signal occurs when these subcarriers experience a deep fade in a frequency selective fading channel. In addition, we show two effective techniques to avoid the performance degradation: random code selection and frequency interleaving; which technique provides a better performance depends on modulation level, code multiplexing order, and presence of channel coding.

In this paper, we propose a spectrally efficient frequency-domain channel estimation scheme suitable for training sequence inserted single-carrier (TS-SC) block transmission using frequency-domain equalization (FDE). The proposed scheme performs the channel estimation in two steps and allows the use of shorter TS (but, longer than the channel length) than the conventional channel estimation schemes. In the first step, the received TS having cyclic property is constructed for performing frequency-domain channel estimation and the improved channel estimate is obtained by using simple averaging of noisy channel estimates. In the second step, the maximum likelihood channel estimation is carried out iteratively by using both the TS and the estimated symbol sequence obtained in the first step. It is shown by computer simulation that the proposed 2-step frequency-domain iterative channel estimation scheme achieves a bit error rate (BER) performance close to perfect channel estimation even in a relatively fast fading environment.

In this paper, joint water filling and maximal ratio transmission (joint WF-MRT) downlink transmit diversity for a single-carrier distributed antenna network (SC DAN) is proposed. The joint WF-MRT transmit weight allocates the transmit power in both transmit antenna dimension and frequency dimension, i.e., the power allocation is done both across frequencies based on WF theorem and across transmit antennas based on MRT strategy. The cumulative distribution function (CDF) of the channel capacity achievable by joint WF-MRT transmit diversity is evaluated by Monte-Carlo numerical computation method. The channel capacities achievable with joint WF-MRT, MRT, and WF transmit weight (WF transmit weight is done across transmit antennas and frequencies based on WF theorem) are compared. It is shown that the joint WF-MRT transmit weight provides the highest channel capacity among three transmit weights.

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.

This paper presents the results of field experiments on the pilot symbol assisted (PSA) coherent multistage interference canceller (COMSIC) receiver in the direct sequence code division multiple access (DS-CDMA) reverse link. The implemented COMSIC receiver comprising three cancellation stages employs PSA channel estimation and replica generation of multiple access interference (MAI) of other users. The experimental results demonstrate that the COMSIC receiver associated with antenna diversity reception and fast transmission power control (TPC) exhibits effectiveness in suppressing severe MAI in actual multipath fading channels. The transmission power of a mobile station (MS) when the COMSIC receiver is employed at a base station (BS) is reduced by approximately 2.0 and 4.0 dB compared to that with the matched filter (MF)-based Rake receiver when the ratios of the target signal energy per bit-to-interference power spectrum density ratio (Eb/I0) of the desired user to the target user are Δtarget= -6 and -9 dB, respectively. Furthermore, for the COMSIC receiver, the transmission power of a MS at the average bit error rate (BER) of 10-3 with antenna diversity is decreased by approximately 7.5 and 11 dB compared to that without antenna diversity when the Δtarget values are -6 and -9 dB, respectively.

An improved pilot symbol-assisted channel estimation filter, called the weighted multi-slot averaging(WMSA)channel estimation filter, is presented for DS-CDMA transmission links using coherent RAKE combining. Known pilot symbols are periodically time-multiplexed with the sequence of transmitted data symbols; they are placed at the beginning of each data slot. The WMSA channel estimation filter extends the observation interval over several slots. The average bit error rate (BER) performance achievable with coherent RAKE combining using the proposed WMSA channel estimation filter is evaluated by computer simulations in a frequency selective multipath Rayleigh fading channel and the results are compared with those achievable with the use of other channel estimation filters such as an interpolation filter. The DS-CDMA reverse link requires fast transmit power control(TPC). In this paper, we also consider fast TPC based on the measurement of signal-to-interference plus background noise ratio(SIR). The average BER performance with the time-multiplexed pilot channel is also compared with that with the parallel pilot channel.

Pilot symbol-assisted (PSA) decision-directed coherent adaptive array diversity (CAAD) is proposed for increasing the reverse link capacity of DS-CDMA mobile radio systems. In the proposed scheme, PSA channel estimation is applied to coherent Rake combining, and the weights of the antenna array are adaptively updated using both pilot symbols and decision-directed data symbols after Rake combining as references for minimum mean squared error (MMSE) criteria. The reverse link capacity of a 3-sectored base station is evaluated by computer simulation when fast transmit power control (TPC) based on singal-to-interference plus backgound noise power ratio (SIR) measurement is applied under nultipath Rayleigh fading environments. It is shown that a 6-element (sector) CAAD receiver can increase the capacity to about 4.2 times that with a single antenna (per sector) receiver when links are interference-limited. The link capacity achievable with the 6-element CAAD receiver is 1.2 times that with a 6-branch antenna diversity reciever with antenna spacing of 10 carrier wavelengths, while significantly reducing the strong interference from high bit rate transmission (high transmit power) users.

Experimental results of 1. 92 Mbps data transmission over a 20 MHz wideband DS-CDMA (W-CDMA) mobile radio link under frequency selective multipath fading are presented. 1. 92 Mbps data were transmitted using an orthogonal multicode transmission scheme. The combined use of antenna diversity reception, RAKE combining, and concatenated channel coding is applied to improve transmission performance. Laboratory and field experimental results demonstrated the possibility of 2 Mbps data transmission in a real fading environment.

In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) especially from high rate users. This paper proposes a fast and accurate two-step beam tracking algorithm implemented in a pilot symbol-assisted coherent adaptive antenna array diversity (CAAAD) receiver and evaluates its performance both by computer simulation and laboratory experiments. In the proposed scheme, the receiver antenna weights are updated by using both the signal-to-interference power ratio (SIR) measurements employing multiple sets of antenna weights (MSAW) and an adaptive algorithm based on the minimum mean square error (MMSE) criterion, in which other sets except for a original set of antenna weights are simply generated by a original set. Computer simulation results show that antenna weights of a four-antenna CAAAD receiver using the proposed beam tracking algorithm tracks changes in the direction of arrival (DOA) of the desired user at up to 34.3 degrees/sec, which corresponds to 215 km/h at 100 m from a base station. We also confirm based on the experiments in a radio anechoic room that the generated antenna weights track the DOA changes up to 12.3 degrees/sec.

This paper addresses an important issue on the spreading bandwidth of direct sequence code division multiple access (DS-CDMA) cellular mobile radio systems: does wider spreading bandwidth provide larger capacity? And if so, to what extent? The capacity of the perfect power controlled reverse link is evaluated by computer simulation for 1.25 MHz and 5 MHz spreading bandwidths under various sets of propagation channel parameters (path loss decay factor, shadowing standard deviation, shadowing correlation, number of resolved propagation paths) and antenna diversity reception.

This paper elucidates through experiments the improvement in the achievable bit error rate (BER) performance when space time transmit diversity (STTD) is applied to the wideband direct sequence code division multiple access (W-CDMA) forward link. First, laboratory experimental results clarify that the received path timing difference of transmitted signals from two antennas, due to the propagation delay, should be within a chip duration of approximately 1/4 and 1/2 with and without fast transmit power control (TPC), respectively, in order to achieve a prominent transmit diversity effect. We show that the required average received signal energy per bit-to-background noise spectrum density (Eb/N0) at the average BER of 10-3 using STTD is decreased by approximately 4.2 (1.7) dB compared to the case of single-antenna transmission at the maximum Doppler frequency, fD, of 5 Hz without (with) antenna diversity reception at a mobile station (MS) due to the increasing randomization effect of burst error. Furthermore, we elucidate that although the gain of STTD in field experiments is decreased compared to that in laboratory experiments, since the degradation in path search accuracy is greater due to the frequently changing delay time of each path in a real multipath-fading channel, the required average received signal energy per bit-to-interference plus background noise power spectrum density ratio (Eb/I0) at the average BER of 10-3 with STTD is decreased by approximately 1.3 to 1.5 (0.7 to 1.0) dB without (with) antenna diversity reception when fast TPC is not applied in the forward link. This indicates that STTD is effective for a channel without TPC such as a common control channel in a real multipath-fading channel.

The reverse-link of the DS-CDMA cellular system requires transmit power control (TPC) and diversity reception. This paper develops the expression of the received signal-to-interference ratio (SIR), and evaluates the outage probability using the Monte Carlo simulation to obtain the link capacity. The link capacities with received signal strength (SS)-based TPC and SIR-based TPC are compared. This paper investigates the required maximum and minimum transmit powers and the capacity gain of the SIR-based TPC over SS-based TPC as well as the effect of the diversity reception on the link capacity and transmit power. The reverse-link capacity is compared with the forward-link capacity to check the balance of capacities between both links.

This paper compares the packet error rate (PER) performance of three access schemes, i.e., single-carrier (SC)/DS-CDMA, multi-carrier (MC)/DS-CDMA, and MC-CDMA assuming an 80-MHz bandwidth in order to achieve an optimum broadband packet wireless access scheme. In a broadband propagation channel, severe multipath interference degrades the accuracy of timing detection of multipath components (path search) and channel estimation required for coherent detection. Computer simulation results show that, in the reverse link, SC/DS-CDMA achieves better performance than MC/DS-CDMA because the pilot signal power in one sub-carrier required for path search and channel estimation decreases as the number of sub-carriers increases. The superiority of MC-CDMA to MC (SC)/DS-CDMA in the forward link is also demonstrated, because frequency diversity is effectively utilized in association with the mitigation of a much longer symbol duration than the delay spread in MC-CDMA, meanwhile a higher degree of multipath interference offsets the Rake time diversity in MC (SC)/DS-CDMA in a broadband multipath fading channel.

This paper experimentally evaluates the bit error rate (BER) performance of single-carrier broadband DS-CDMA (B-CDMA) scheme using a 100-MHz bandwidth (chip rate of 81.92 Mcps) in frequency-selective multipath fading channels. The achievable information bit rate is 20.36 (2.5) Mbps when the spreading factor (SF) is SF = 4 (32). In order to achieve a high data-rate transmission with high quality (i.e., average BER is below 10-6), we apply pilot symbol-assisted coherent Rake receiving with a large number of Rake fingers (maximum number of Rake fingers is SF2), 2-branch antenna diversity reception, convolutional coding, and signal-to-interference power ratio (SIR) measurement-based fast closed-loop transmit power control (TPC). Experimental results show that the average BER of 10-6 for the 20.36 (2.5)-Mbps transmission is achieved at the required average transmit Eb/N0 of approximately 6.7 (5.0) dB when the number of multipaths is L = 2 and the maximum fading Doppler frequency is fD = 20 Hz. We also show that Rake time diversity and fast TPC are effective in a broadband propagation channel where many resolvable paths (such as 12 paths) are observed.

This paper evaluates through laboratory and field experiments the combined effect of the coherent adaptive antenna array diversity (CAAAD) receiver and signal-to-interference plus background noise ratio (SINR)-based fast transmit power control (TPC) in order to improve performance beyond that of space diversity (SD) with maximal ratio combining (MRC) in all low-to-high signal-to-interference power ratio (SIR) channels in the W-CDMA reverse link. Although the previously proposed CAAAD receiver comprising an adaptive antenna array based on the minimum mean square error (MMSE) criterion and a coherent Rake combiner was very effective in suppressing interference in low SIR (interference is severe) channels, SD employing MRC in noise limited channels (high SIR) outperformed the CAAAD because of its uncorrelated reception of fading variation due to its large antenna separation. The laboratory experimental results showed that the required average transmit signal energy per bit-to-background noise spectrum density (Eb/N0) with the CAAAD receiver using fast TPC is lower than that with an SD receiver over a wide range of maximum Doppler frequency values from fD = 5 Hz to 500 Hz in a low-to-high SIR channel. The results of the field experiments also showed that combining CAAAD and fast TPC is a powerful means to reduce severe multiple access interference (MAI) from high rate users in a low-to-high SIR environment and is more effective than using the SD receiver with the same number of antennas, i.e., the measured BER was improved by approximately one order of magnitude, when the relative transmit power of the desired user was 8 dB with two antennas at the average received SIR at the antenna input of -12 dB.

This paper proposes an inter-cell site diversity scheme based on 2-step selection combining (SC) and investigates through experimentation the effect of inter-cell site diversity in the transmit power-controlled wideband direct sequence code division multiple access (W-CDMA) reverse link. In the proposed algorithm, the decoded data sequence after soft-decision Viterbi decoding at each base station (BS) is transferred via the backhaul (wired line between BS and radio network controller (RNC) simulator) to the RNC simulator accompanied by reliability information of cyclic redundancy check (CRC) results per frame and the average signal-to-interference power ratio (SIR) calculated over the interleaving interval. The 2-step SC for each frame is performed at the RNC simulator using these two types of reliability information. We conclude from the laboratory experiments that the transmit power of a mobile station (MS) can be decreased since the selection period, TSEL, is shorter irrespective of the interleaving length, TILV, and that the required transmit power of a MS satisfying the average BER of 10-3 in inter-cell site diversity among 2 and 3 cell sites can be decreased by approximately 1.0 (0.5) dB and 1.3 (0.7) dB for fading maximum Doppler frequency fD = 5 (80) Hz, respectively, compared to a one-site connection (TILV = 80 msec, TSEL = 10 msec, path loss difference between 2 BSs and MS is 0 dB). We also confirmed by field experiments that the required transmit power of a MS in inter-cell site diversity between 2 cell sites can be decreased by approximately 2.0 dB compared to that of a one-site connection.