A DS-CDMA mobile communication system accommodating multi-class users is considered. The number of supportable users depends on the distributions of data rate and required communication quality among users. Simple expressions for the reverse link capacity with transmit power control, antenna diversity, and rake combining, are derived for a single-cell system and a multi-cell system.

This paper addresses a classic question about whether transmit power control (TPC) can increase the spectrum efficiency of a TDMA system and an FDMA cellular system as in the case of a DS-CDMA cellular system. Two types of TPC schemes are considered; one is slow TPC that regulates the distance dependent path loss and shadowing loss, while the other is fast TPC that regulates multipath fading as well as path loss and shadowing loss. In addition to TPC, antenna diversity reception is considered. The allowable interference rise factor χ, which is defined as the interference plus background noise-to-background noise power ratio, is introduced. The simple expressions for the signal-to-interference plus background noise power ratio (SINR) at the diversity combiner output using maximal-ratio combining (MRC) are derived to obtain the reuse distance by computer simulations. The impact of joint use of TPC and antenna diversity reception on the spectrum efficiency is discussed. It is found that the joint use of fast TPC and antenna diversity is advantageous and larger spectrum efficiency can be achieved than with no TPC. On the other hand, the use of slow TPC is found advantageous only for small values of standard deviation of shadowing loss; however, the improvement in the spectrum efficiency is quite small.

This paper evaluates the effect of inter-sector diversity with maximal ratio combining (MRC) coupled with coherent Rake combining and 2-branch antenna diversity reception in the transmit-power-controlled wideband direct sequence code division multiple access (W-CDMA) reverse link. We first elucidate based on laboratory experiments that the required average transmit signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average bit error rate (BER) of 10-3 with inter-sector diversity using two sectors is decreased by approximately 1.4, 1.0, and 0.2 dB compared to that with inter-cell site diversity using two cell sites with antenna diversity reception due to the superiority of MRC to selection combining (SC), when the difference in the average path loss between a base station (BS) and a mobile station (MS) is Δ12 = 0, 3, and 6 dB, respectively. We also clarify in actual field experiments that the inter-sector diversity associated with Rake time diversity and antenna diversity further decreases the required average transmit power of a MS if the number of resolved paths is small such as 1 or 2 in each sector reception, even when the fading correlation between sectors is relatively large. Furthermore, we show that the required average transmit power of a MS for satisfying the average BER of 10-3 with inter-sector diversity is decreased above approximately 2.0-2.5 dB compared to that with one-sector reception, owing to the significantly increased inter-sector diversity effect in addition to the Rake time diversity and antenna diversity, when the fading correlation averaged over the measurement course is approximately 0.7.

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.

This paper proposes an outer loop control method of fast transmit power control (TPC) for high-quality data transmission such as that with the average bit error rate (BER) of 10-6 in serial concatenated channel coding combining convolutional (inner) and Reed-Solomon (outer) codings for DS-CDMA mobile radio. In the proposed method, the outer loop control is performed based on the measured intermediate block error rate (BLER) value after inner-channel decoding. Since the number of block errors after inner-channel decoding is much greater than that of the final output after outer channel decoding, fast tracking performance of the sudden changes in the propagation conditions such as the number of multipaths and fading Doppler frequency, i.e., moving speed of the mobile station, is achieved. The experimental results clarify that the measured BLER after outer channel decoding is accurately controlled to almost a constant value from the low to high fading maximum Doppler frequency of up to 480 Hz, and that the measured BER after outer channel decoding is within the range of one-order of magnitude of the antenna diversity reception (meanwhile, the target SIR value after Rake combining varied with the range of 2.5 dB).

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.

This paper proposes a measurement scheme of instantaneous signal-to-average interference plus background noise ratio (SIR) for SIR-based fast transmit power control (TPC) using time-multiplexed pilot symbols on the reverse link of DS-CDMA mobile radio. Both pilot and data are used for signal power measurement, but pilot symbols are used for measurement of average interference plus noise power. By the means of computer simulation, the TPC parameters, i. e. , SIR measurement period and step size, are optimized to maximize the link capacity in a Rayleigh fading environment. The capacity of the power controlled reverse link with channel coding and Rake combining is evaluated to understand the effects of the number of resolvable propagation paths, fading maximum Doppler frequency(or mobile traveling speed), and antenna diversity reception in single-cell and multi-cell environments.

Field experiments using the 2 GHz carrier frequency band were conducted nearby Tokyo to evaluate the effect of joint use of Rake combining and antenna diversity and also the effect of spreading chip rate (or bandwidth) on the achievable bit error rate (BER) performance and the mobile station transmit power distribution of power controlled coherent DS-CDMA reverse-link (mobile-to-base). Four chip rates, 0. 96, 1. 92, 3. 84, and 7. 68 Mcps, were used. The command interval and power step size of the fast transmission power control (TPC) used in the experiments, 1. 25 ms and 1 dB, respectively, were based on measurements of signal-to-interference plus background noise power ratio (SIR) after Rake combining. The field experiments demonstrate that the joint use of antenna diversity and Rake combining significantly improves the BER performance and, furthermore, that increasing the chip rate improves the BER performance and decreases the transmit power because of enhanced Rake combining through an increase in the number of resolved paths.

Fast transmit power control (TPC) adaptively controls the mobile terminal transmit power so that the instantaneous signal-to-interference plus background noise ratio's (SIR's) of received signals of all users at the base station receiver are kept at the target value to avoid the adverse effect of multipath fading as well as the near/far problem. This paper theoretically analyzes the power efficiency of power controlled DS-CDMA reverse link assuming ideal Rake combining under multi-user and multipath Rayleigh fading environments. The achievable bit error rate (BER) performance is evaluated as a function of average and peak transmit powers required at mobile terminals. The effect of number of resolved paths is discussed. It is shown that the required peak transmit power with fast TPC is larger than that without fast TPC for relatively large BER values; however, when the link is interference-limited, fast TPC achieves significantly larger link capacity.

A simplified analysis is presented for the reverse link capacity of DS-CDMA mobile radio with transmit power control (TPC) based on measurement of signal-to-interference plus background noise (SIR) when users require different levels of quality. The link capacity is defined as the maximum achievable sum of the required SIRs, and the increase in transmit power due to SIR-based TPC is discussed. Also analyzed is the total link capacity when narrowband DS-CDMA systems share the radio spectrum of a wideband system. The capacity loss due to non-uniform use of the spectrum is discussed.