This paper investigates based on laboratory experiments the multiuser interference suppression effect of the coherent adaptive antenna array diversity (CAAAD) receiver employing an optical fiber feeder in the intermediate frequency (IF) stage, aiming at the practical use of adaptive antenna array beam forming techniques based on the W-CDMA air interface. We employed a configuration in which the optical fiber conversion, i.e., electrical-to-optical (E/O) conversion (vice versa (O/E)), is performed on a received signal amplified by an automatic gain control (AGC) amplifier in the IF stage, to abate the impact of the noise component generated by the E/O (O/E) converters. We first show by computer simulation the superiority of the optical fiber conversion in the IF stage to that in the radio frequency (RF) stage based on the achievable bit error rate (BER) performance. Furthermore, experimental results elucidate that the loss in the required transmit signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) of the implemented CAAAD receiver at the average BER of 10-3 employing the optical fiber feeders in the IF stage compared to that with coaxial cables is within a mere 0.2 dB (six antennas, three users, two-path Rayleigh fading channel model, and the ratio of the target signal energy per bit-to-interference power spectrum density ratio (Eb/I0) of the desired user to that of the interfering users for fast transmission power control (TPC) is ΔEb/I0=-15 dB).

This paper presents laboratory and field experimental results of the coherent adaptive antenna array diversity (CAAAD) receiver employing receiver antenna-weight generation common to all Rake-combined paths (hereafter path-common weight generation method) in the W-CDMA reverse link, in order to elucidate the suitability of the path-common weight generation method in high-elevation antenna environments such as cellular systems with a macrocell configuration. Laboratory experiments using multipath fading simulators and RF phase shifters elucidate that even when the ratio of the target Eb/I0 of the desired to interfering users is Δ Eb/I0=-12 dB, the increase in the average transmit Eb/N0 employing the CAAAD receiver coupled with fast transmission power control (TPC) using outer-loop control from that for Δ Eb/I0=0 dB is within only 1.0 dB owing to the accurate beam and null steering associated with fast TPC. Furthermore, field experiments demonstrate that the required transmission power at the average block error rate (BLER) of 10-2 employing the CAAAD receiver with four antennas is reduced by more than 2 dB compared to that using a four-branch space diversity receiver using maximum ratio combining (MRC) with the fading correlation between antennas of 0 when Δ Eb/I0=-15 dB and that the loss in the required transmission power of the CAAAD receiver in the same situation as that in a single-user environment is approximately 1 dB. The field experimental results in an actual propagation environment suggest that the CAAAD receiver is effective in suppressing multiple access interference, thus decreasing the required transmission power when the gap in the direction of arrival between the desired user and interfering users is greater than approximately 20 degrees.

This paper proposes physical channel structures and a cell search method for OFDM based radio access in the Evolved UTRA (UMTS Terrestrial Radio Access) downlink, which supports multiple scalable transmission bandwidths from 1.25 to 20 MHz. In the proposed physical channel structures, the central sub-carrier of the OFDM signal is located on the frequency satisfying the 200-kHz raster condition regardless of the transmission bandwidth of the cell site. Moreover, the synchronization channel (SCH) and broadcast channel (BCH), which are necessary for cell search, are transmitted in the central part of the entire transmission spectrum with a fixed bandwidth. In the proposed cell search method, a user equipment (UE) acquires the target cell in the cell search process in the initial or connected mode employing the SCH and possibly the reference signal, which are transmitted in the central part of the given transmission bandwidth. After detecting the target cell, the UE decodes the common control information through the BCH, which is transmitted at the same frequency as the SCH, and identifies the transmission bandwidth of the cell to be connected. Computer simulations show the fast cell search performance made possible by using the proposed SCH structure and the cell search method.

Transmit beamforming can exploit the spatial diversity afforded by multiple-input multiple-output (MIMO) systems with low complexity. To apply this technique in more practical systems with the constraint of limited feedback, codebook based beamforming and vector quantization technique have been considered in various papers. On the other hand, multi-user scheduling is able to achieve another form of diversity arising from the independence of fading for different users, however, has not been fully taken into account in existing codebook based beamforming schemes. In this letter, a multi-codebook based beamforming and scheduling scheme is proposed, which exploits both spatial diversity and multi-user diversity by switching the codebook for different resource blocks. Meanwhile, the multi-codebook design issue is addressed, the corresponding theoretical analysis is provided, and the performance gain of proposed scheme is simulated. Furthermore, the impacts of related parameters on the performance gain are also investigated.

This paper presents laboratory experimental results on the throughput performance when key techniques such as adaptive modulation and channel coding (AMC) and hybrid automatic repeat request (ARQ) with packet combining are employed by an implemented transceiver based on the High-Speed Downlink Packet Access (HSDPA) air interface in a multipath fading channel. In AMC operation, we applied four modulation and coding schemes (MCSs): MCS1 (QPSK data modulation with the channel coding rate of R = 1/2, hereafter simply referred to as QPSK with R = 1/2), MCS2 (QPSK with R = 3/4), MCS3 (16 QAM with R = 1/2), and MCS4 (16 QAM with R = 3/4). The results elucidate that a peak average throughput above 5.0 Mbps is achieved at the average received signal energy per chip-to-background noise power spectrum density ratio (Ec/N0) of more than approximately 20 dB in a one-path fading channel; nevertheless, the achievable peak throughput becomes approximately 2.9 (2.6) Mbps due to severe multipath interference (MPI) in a two-path fading channel where the average signal power of the second path is 6 (3) dB lower than that of the first path, assuming nine-code-channel multiplexing with the fading maximum Doppler frequency of fD = 5 Hz. Furthermore, we clarify that although the throughput performance employing Type-II hybrid ARQ (i.e., Incremental redundancy) is almost the same as that employing Type-I hybrid ARQ with packet combining (i.e., Chase combining) in a two-path fading channel, Incremental redundancy exhibits superiority over Chase combing in a one-path fading channel for a high Doppler frequency channel such as fD = 80 Hz.

This paper proposes a three-step cell search algorithm that utilizes only the common pilot channel (CPICH) in the forward link and employs spreading by a combination of a cell-specific scrambling code (CSSC) and an orthogonal short code for Orthogonal Frequency and Code Division Multiplexing (OFCDM) broadband packet wireless access. In the proposed cell search algorithm, the OFCDM symbol timing, i.e., Fast Fourier Transform (FFT) window timing, is estimated by detecting the guard interval timing in the first step. Then, in the second step, the frame timing and CSSC group are simultaneously detected by taking the correlation of the CPICH based on the property yielded by shifting the CSSC phase in the frequency domain. Finally, the CSSC within the group is identified in the third step. The most prominent feature of the proposed cell search algorithm is that it does not employ the conventional synchronization channel (SCH), which is exclusively used for the cell search. Computer simulation results elucidate that when the transmission power ratio of the CPICH to one code channel of the traffic channel (TCH) is 12 dB, the proposed cell search method achieves faster cell search time performance compared to the conventional method using the SCH with the transmission power ratio of the SCH to one code channel of the TCH of 6 dB. Furthermore, the results show that it can accomplish the cell search within 1.7 msec at 95% of the locations in a 12-path Rayleigh fading channel with the maximum Doppler frequency of 80 Hz and the r.m.s. delay spread of 0.32 µs.

This paper proposes a three-step cell search algorithm utilizing a synchronization channel (SCH) and common pilot channel (CPICH) in the forward link for OFCDM (Orthogonal Frequency and Code Division Multiplexing) broadband packet wireless access, and evaluates the cell search time performance by computer simulation. In the proposed three-step cell search algorithm, the OFCDM symbol timing, i.e., Fast Fourier Transform (FFT) window timing is estimated employing SCH or guard interval (GI) correlation in the first step. Then, the frame timing is detected by employing the SCH and the cell-specific scrambling code (CSSC) is identified by the CPICH in the second and third steps, respectively. Computer simulation results elucidate that the proposed three-step cell search algorithm achieves fast cell search time performance, i.e., cell detection probability of 90% within approximately 50 msec, assuming the number of CSSCs of 512 in a 19 hexagonal-cell model. We also clarify that there is no prominent difference in cell search time performance between the two employed SCH structures, time-multiplexed and frequency-multiplexed, assuming that the total transmit power of the SCH is the same. Based on the comparison of four substantial cell search algorithms, the GI-plus-SCH correlation method, in which FFT windowing timing detection, frame timing detection, and CSSC identification are performed by GI correlation, frequency-multiplexed SCH, and CPICH, respectively, exhibits the cell search time of approximately 44 msec at the detection probability of 90% with an optimized averaging parameter in each step.

This paper presents a multipath interference canceller (MPIC) configuration based on multipath interference (MPI) replica generation per transmit antenna (called PTA-MPIC). This configuration is associated with Space Time Transmit Diversity (STTD) for the common control physical channel (CCPCH), which takes advantage of tentative decision data after STTD decoding, and with closed-loop type phase control (PC) transmit diversity for the dedicated physical channel (DPCH) employing tentative decision data after diversity combining, in the W-CDMA forward link. This paper also proposes transmitter carrier phase verification, i.e., an antenna verification method used in PC transmit diversity, that utilizes the dedicated pilot symbols in a DPCH after the PTA-MPIC removes the MPI components. The one-stage PTA-MPIC removes the MPI from the common pilot channel (CPICH), the CCPCH, and the synchronization channel (SCH). The simulation results show that this canceller reduces the required average transmit Eb/N0 of the DPCH at the average BER of 10-3 by approximately 3.0 dB compared to that using a MF-based Rake receiver (the transmit power ratio of each common channel to DPCH is RCPICH/DPCH = 3 dB, RCCPCH/DPCH = 5 dB, and RSCH/DPCH = 3 dB, with TPC and without antenna diversity reception at the user equipment). Furthermore, it is shown that in the two-stage PTA-MPIC with MPI suppression for all channels associated with PC transmit diversity, the required average transmit Eb/N0 employing the proposed antenna verification is reduced by approximately 0.3 dB, 0.5 dB, and 1.2 dB compared to that using the conventional antenna verification when the transmission power ratio of the interfering DPCH to the desired DPCH is RInt/Des = 0 dB, 3 dB, and 6 dB for ten DPCHs. This is because the number of detection errors of the transmitted carrier phase in the second antenna due to feedback information bit decoding error is reduced.

This paper presents the best transmit diversity schemes for three types of common/shared control signals from the viewpoint of the block error rate (BLER) performance in the Evolved UTRA downlink employing OFDM radio access. This paper also presents the coverage performance of the common/shared control signals using transmit diversity with respect to the outage probability that satisfies the required BLER performance, which is a major factor determining the cell configuration. Simulation results clarify that Space-Frequency Block Code (SFBC) and the combination of SFBC and Frequency Switched Transmit Diversity (FSTD) are the best transmit diversity schemes among the open-loop type transmit diversity candidates for two-antenna and four-antenna transmission cases, respectively. Furthermore, we show through system-level simulations that SFBC is very effective in reducing the outage probability at the required BLER for the physical broadcast channel (PBCH), for the common control signal with resource block (RB)-level assignment such as the dynamic broadcast channel (D-BCH) and paging channel (PCH), and in increasing the number of accommodated L1/L2 control signals over one transmission time interval duration, using mini-control channel element (CCE)-level assignment.

This paper presents the effect of transmit diversity on the initial and neighboring cell search time performance and the most appropriate transmit diversity scheme based on system-level simulations employing synchronization signals for the Long Term Evolution (LTE) downlink. The synchronization signals including the primary synchronization signal (PSS) and secondary synchronization signal (SSS) are the first physical channel that a set of user equipment (UE) acquires at the initial radio-link connection. The transmit diversity candidates assumed in the paper are Precoding Vector Switching (PVS), Cyclic Delay Diversity (CDD), Time Switched Transmit Diversity (TSTD), and Frequency Switched Transmit Diversity (FSTD), which are all suitable for simple blind detection at a UE. System-level simulation results show that transmit diversity is effective in improving the detection probabilities of the received PSS timing and PSS sequence in the first step and those of the SSS sequence and radio frame timing in the second step of the cell search process. We also show that PVS achieves fast cell search time performance of less than approximately 20ms at the location probability of 90% regardless of the inter-cell site distance up to 10km. Hence, we conclude that PVS is the best transmit diversity scheme for the synchronization signals from the viewpoint of decreasing the initial and neighboring cell search times.

This paper experimentally demonstrates the possibility of 2-Mbps data transmission using a 5-MHz bandwidth (chip rate of 4.096 Mcps) wideband DS-CDMA (W-CDMA) mobile radio link in frequency-selective multipath fading environments. To reduce the mobile station transceiver complexity, three-orthogonal code multiplexing with the spreading factor (SF) of 4 is employed. In such a small SF transmission, the increased multipath interference (MPI) significantly degrades the transmission performance. We consider two-branch antenna diversity reception and fast transmit power control (TPC) as well as channel coding to mitigate the influence of MPI. Laboratory experimental results show that the use of antenna diversity reception is significant and that the fast TPC improves the transmission performance. Furthermore, the impact of the fading maximum Doppler frequency, fD, and that of the channel coding interleaving size, Tint, on the achievable BER performance are also investigated.

This paper proposes a fast target cell search algorithm used during intermittent reception in the idle mode of a mobile station (MS) for inter-cell asynchronous W-CDMA mobile radio. In the proposed scheme, since the base station (BS) informs a MS of the relative average received timing differences between the scrambling code of its BS and those of the surrounding BSs in addition to the scrambling codes, the MS only has to search over the restricted timing duration for the informed scrambling codes. Therefore, the target cell search (i.e., in which the number of candidate cells is limited) can be achieved as fast as in inter-cell synchronous systems. A computer simulation demonstrates that the target cell search time per one super frame (= 720 msec) at the cell detection probability of 95% is accomplished within 5.9 msec (this corresponds to the intermittent time ratio required for the target cell search to become 0.82%), when the transmit power ratios of the common pilot channel (CPICH) and common control physical channel (CCPCH) required for cell search to a dedicated traffic channel (DTCH) are 3 and 6 dB, respectively. In this simulation, the average power delay profile was generated by averaging the instantaneous ones (it was coherently accumulated pilot signal over a 512-chip duration (= 125 µsec) using 4 correlators) over a period of three super frames for 19 target cell-site candidates using the search window with a 10-chip duration (= 2.4 µsec).

This paper presents the fast cell search time performance based on laboratory and field experiments of a 2-step cell search algorithm that uses scrambling code masking for inter-cell asynchronous wideband DS-CDMA (W-CDMA) mobile radio. The scrambling code is masked at different time positions during each scrambling period on the forward-link common control channel (CCH) to detect the scrambling code timing at the mobile receiver. Experiments were conducted using the CCH-to-dedicated traffic channel (DTCH) power ratio, R of 3 dB, 10 DTCHs, and 16 scrambling codes in a single-cell and two-cell models. The field experimental results show that the cell search time of about 600 msec was achieved in vehicular environments at the detection probability of 90% and the average received Eb/N0 (N0 is the background noise without interference) of 13-15 dB for DTCH, even in the worst case scenario when the received signal power ratios of the CCH from two cell sites were 0 dB. The cell search time that was achieved with the 3-step cell search algorithm previously proposed by the authors is estimated from the experimental results; the cell search can be accomplished within about 720 msec at a probability of 96% for 512 scrambling codes and 16 scrambling code groups.

In DS-CDMA (including W-CDMA), a received signal can be resolved into multiple paths to be Rake combined. An important design problem of the Rake receiver is how to accurately search the paths with a sufficiently large signal-to-interference plus background noise power ratio (SIR). This paper investigates the performance of a coherent Rake receiver using pilot symbol-assisted channel estimation with fast transmit power control, and thereby optimizes three key parameters: the total averaging period, Tavg, consisting of a combination of coherent summation and power summation; each period of the summations for measuring the average power delay profile; and path-selection threshold M from the generated power delay profile. We used a path search algorithm, which searches the paths that have M times greater average signal power than the interference plus background noise power measured in the average power delay profile generated using time-multiplexed pilot symbols. It was clarified by both simulation and laboratory experiments that when M = 4, Tavg = 50-100 msec, and the number of slots for coherent accumulation R = 2, the required average transmit Eb/N0 for obtaining the average BER of 10-3 is almost minimized with and without antenna diversity for both ITU-R Vehicular-B and average equal power L-path delay profile model, in which each path suffered independent Rayleigh fading. The paper also shows that based on the field experiments, the path search algorithm with optimized path-selection parameters is robust against actual dynamic changes in the power delay profile shape.

This paper proposes an adaptive selection algorithm for the surviving symbol replica candidates (ASESS) based on the maximum reliability in maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) for Orthogonal Frequency Division Multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing. In the proposed algorithm, symbol replica candidates newly-added at each stage are ranked for each surviving symbol replica from the previous stage using multiple quadrant detection. Then, branch metrics are calculated only for the minimum number of symbol replica candidates with a high level of reliability using an iterative loop based on symbol ranking results. Computer simulation results show that the computational complexity of the QRM-MLD employing the proposed ASESS algorithm is reduced to approximately 1/4 and 1/1200 compared to that of the original QRM-MLD and that of the conventional MLD with squared Euclidian distance calculations for all symbol replica candidates, respectively, assuming the identical achievable average packet error rate (PER) performance in 4-by-4 MIMO multiplexing with 16QAM data modulation. The results also show that 1-Gbps throughput is achieved at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) per receiver antenna of approximately 9 dB using the ASESS algorithm in QRM-MLD associated with 16QAM modulation and Turbo coding with the coding rate of 8/9 assuming a 100-MHz bandwidth for a 12-path Rayleigh fading channel (root mean square (r.m.s.) delay spread of 0.26 µs and maximum Doppler frequency of 20 Hz).

This paper evaluates the bit error rate (BER) performance of high rate data transmission such as at 64 and 384 kbits/s (kbps) with high quality (average BER is below 10-6) using turbo/convolutional coding associated with Rake time diversity, antenna diversity, and fast transmission power control (TPC) in multipath fading channels for W-CDMA mobile communications. Laboratory experiments using multipath fading simulators elucidate the superiority of turbo coding over convolutional coding when the channel interleaving length is 40 msec. The required average transmission power for the average BER of 10-6 using turbo coding is decreased by approximately 1.1-1.5 dB and 1.5-1.6 dB for 64 and 384 kbps data transmissions, respectively, compared to that using convolutional coding for a two-path Rayleigh fading channel with the fading maximum Doppler frequency of fD = 5-200 Hz. Furthermore, field experimental results elucidate that the required transmission power for the average BER of 10-6 employing turbo coding is decreased by approximately 0.6 dB and 2.0 dB compared to convolutional coding for 64 and 384 kbps data transmissions, respectively, without antenna diversity reception, while that with antenna diversity reception exhibits only an approximate 0.3-0.5 dB decrease. This decrease in improvement with antenna diversity reception indicates that in an actual fading channel in the field experiments, the impact of the error in path search for Rake combining and SIR measurement for fast TPC diminishes the performance improvement of the turbo coding due to a very low received signal power.

This paper presents a new adaptive peak-to-average power ratio (PAPR) reduction method based on clipping and filtering (CF) for precoded orthogonal frequency division multiplexing (OFDM)-multiple-input multiple-output (MIMO) transmission. While the conventional CF method adds roughly the same interference power to each of the transmission streams, the proposed method suppresses the addition of interference power to the streams with good channel conditions. Since the sum capacity is dominated by the capacity of the streams under good channel conditions and the interference caused by the PAPR reduction process severely degrades the achievable capacity for these streams, the proposed method significantly improves the achievable sum capacity compared to the conventional CF method for a given PAPR. Simulation results show the capacity gain by using the proposed method compared to the conventional method.

This paper proposes the use of inter-cell transmission power control (TPC) with overload indicator (OLI) signaling to user equipment (UE) in addition to intra-cell TPC for the Evolved UTRA uplink. In the proposed inter-cell OLI transmission method, a cell site (Node B) selects UEs offering high-level interferences to the cell site based on the measured path loss difference, and then, the cell site transmits the OLI signal to the selected UEs. The simulation results show that the inter-cell TPC improves both the average user throughput and cell-edge user throughput at 5% in the cumulative distribution function (CDF) curve, assuming the same sector throughput. For instance, when the sector throughput is 1 Mbps using 1.08 MHz bandwidth, the inter-cell TPC with the proposed UE-common OLI scheme increases the average user throughput and the 5%-cell edge user throughput by approximately 41% and 53%, respectively, compared to the case with intra-cell TPC only. Furthermore, when the inter-cell TPC with the proposed UE-individual OLI is employed, the corresponding average user throughput and the 5% user throughput are increased by approximately 87% and 94%, respectively.

We investigate non-orthogonal multiple access (NOMA) with a successive interference canceller (SIC) in the cellular multiple-input multiple-output (MIMO) downlink for systems beyond LTE-Advanced. Taking into account the overhead for the downlink reference signaling for channel estimation at the user terminal in the case of non-orthogonal multiuser multiplexing and the applicability of the SIC receiver in the MIMO downlink, we propose intra-beam superposition coding of a multiuser signal at the transmitter and the spatial filtering of inter-beam interference followed by the intra-beam SIC at the user terminal receiver. The intra-beam SIC cancels out the inter-user interference within a beam. Regarding the transmitter beamforming (precoding), in general, any kind of beamforming matrix determination criteria can be applied to the proposed NOMA method. In the paper, we assume open loop-type random beamforming, which is very efficient in terms of the amount of feedback information from the user terminal. Furthermore, we employ a weighted proportional fair (PF)-based resource (beam of each frequency block and power) allocation for the proposed method. Simulation results show that the proposed NOMA method using the intra-beam superposition coding and SIC simultaneously achieves better sum and cell-edge user throughput compared to orthogonal multiple access (OMA), which is widely used in 3.9 and 4G mobile communication systems.

This paper investigates the performance of interleave division multiple access (IDMA)-based random access with various interference canceller structures in order to support massive machine-type communications (mMTC) in the fifth generation (5G) mobile communication system. To support massive connectivity in the uplink, a grant-free and contention-based multiple access scheme is essential to reduce the control signaling overhead and transmission latency. To suppress the packet loss due to collision and to achieve multi-packet reception, non-orthogonal multiple access (NOMA) with interference cancellation at the base station receiver is essential. We use IDMA and compare various interference canceller structures such as the parallel interference canceller (PIC), successive interference canceller (SIC), and their hybrid from the viewpoints of the error rate and decoding delay time. Based on extensive computer simulations, we show that IDMA-based random access is a promising scheme for supporting mMTC and the PIC-SIC hybrid achieves a good tradeoff between the error rate and decoding delay time.