Partial capture effect for multi-carrier radio packet communication network is evaluated in frequency selective fading channel. In multi-carrier modulation (MCM) network where each terminal uses several sub-carriers for transmission,the terminals have different instantaneous frequency responses because of its location, fading pattern, and other various factors. This generates the difference of received power in frequency domain, then partial capture effect can be considered at each sub-carrier. Moreover these partially captured packets are not damaged by inter symbol interference (ISI) caused by frequency selective fading, which seriously degrades single-carrier modulation (SCM) network. From this point of view we present the partial capture effect for the MCM network in the frequency selective fading environment. The results show that the MCM network with partial capture has more advantages than the MCM network without partial capture in terms of the throughput and the average number of transmissions.

This paper presents a comparison of the throughput performance employing hybrid automatic repeat request (HARQ) with packet combining, such as Type-I with packet combining (simply Chase combining hereafter) and Type-II (Incremental redundancy hereafter), using turbo coding in a multipath fading channel in high speed downlink packet access (HSDPA). We apply a multipath interference canceller (MPIC) to remove the influence of severe multipath interference. Link level simulation results show that the maximum throughput using Incremental redundancy with 64QAM is improved by approximately 5-8% compared to that using Chase combining, and that the required average received signal energy of 12 code channels per chip-to-background noise spectrum density (Ec/N0) at the throughput of 4 Mbps with Incremental redundancy is decreased by approximately 1.0 dB rather than that with Chase combining when the vehicular speed is higher than approximately 30 km/h. Furthermore, we elucidate based on the system level simulation that although no improvement is obtained in a slow mobility environment such as the average vehicular speed of 3 km/h, the achieved throughput of Incremental redundancy is increased by approximately 5-6% and 13% for the average vehicular speed of 30 km/h and 120 km/h, respectively, compared to that with Chase combining.

This paper presents experimental evaluations of the effect of time diversity obtained by hybrid automatic repeat request (HARQ) with soft combining in space and path diversity schemes on orthogonal frequency division multiplexing (OFDM)-based packet radio access in a downlink broadband multipath fading channel. The effect of HARQ is analyzed through laboratory experiments employing fading simulators and field experiments conducted in downtown Yokosuka near Tokyo. After confirming the validity of experimental results based on numerical analysis of the time diversity gain in HARQ, we show by the experimental results that, for a fixed modulation and channel coding scheme (MCS), time diversity obtained by HARQ is effective in reducing the required received signal-to-interference plus noise power ratio (SINR) according to an increase in the number of transmissions, K, up to 10, even when the diversity effects are obtained through two-branch antenna diversity reception and path diversity using a number of multipaths greater than 12 observed in a real fading channel. Meanwhile, in combined use with the adaptive modulation and channel coding (AMC) scheme associated with space and path diversity, we clarify that the gain obtained by time diversity is almost saturated at the maximum number of transmissions in HARQ, K ' = 4 in Chase combining and K ' = 2 in Incremental redundancy, since the improvement in the residual packet error rate (PER) obtained through time diversity becomes small owing to the low PER in the initial packet transmission arising from appropriately selecting the optimum MCS in AMC. However, the experimental results elucidate that the time diversity in HARQ with soft combining associated with antenna diversity reception is effective in improving the throughput even in a broadband multipath channel with sufficient path diversity.

In this paper, Orthogonal Multicode OFDM-DS/CDMA system using Partial Bandwidth Transmission is proposed. By using the flexible carrier allocation of OFDM, Partial Bandwidth Transmission is considered for high quality communication. Furthermore, multicode packet data transmission is presented. Multicode packet data transmission is very effective to handle variable data. Since the proposed system can detect the header information without complex control, it is also suitable for packet data transmission. The computer simulation results show that the BER performance of the proposed system with the ideal channel estimation is improved compared with the case of the conventional Orthogonal Multicode DS/CDMA system with ideal RAKE receivers. Moreover the proposed system with the channel estimation by MLS algorithm also shows the good BER performance. In packet data transmission, the delay and throughput performances are also improved in the proposed system.

This paper proposes a new cell-specific scrambling code (CSSC) assignment method and a fast cell search algorithm in the forward link for Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access that are suitable for a system incorporating coexisting isolated and cellular cells. In the proposed method, one or some CSSC groups and thereby the CSSCs belonging to the CSSC groups are exclusively assigned to isolated cells. By detecting the best CSSC assigned to an isolated cell with higher priority than the cellular cells, the best cell including the isolated cell obtaining the minimum path loss can be detected far faster than by using the conventional cell search method, which employs uniform CSSC assignment. Computer simulation results show that by using the proposed cell search method together with the exclusive CSSC assignment to the isolated cells, the isolated-cell detection probability of approximately 90% is achieved at the cell boundary after the cell search time of 10 msec, while corresponding detection probability using conventional CSSC assignment is approximately 80% without notifying the user equipment of the cell type and its CSSC information of the surrounding cells via the broadcast channel, at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) of 10 dB for the common pilot channel (CPICH) in the cellular cells, when the transmission power ratio of the CPICH to the packet data channel (PDCH) for a one-code channel is RCPICH = 9 dB in a 20-cell layout model.

This paper proposes Variable Spreading and Chip Repetition Factors (VSCRF)-Code Division Multiple Access (CDMA) broadband packet wireless access in the reverse link, which flexibly supports employing the same air interface in various radio environments such as a cellular system with a multi-cell configuration and local areas such as very-small cell, indoor, and isolated-cell environments. In VSCRF-CDMA, we propose two schemes: the first is a combination of time-domain spreading with an orthogonal code and chip repetition that achieves orthogonal multiple access in the frequency domain by utilizing a comb-shaped frequency spectrum, and the other is adaptive control of the spreading factor and chip repetition factor according to the cell configurations, number of simultaneously accessing users, propagation channel conditions, and major radio link parameters. Simulation results show that the proposed VSCRF-CDMA associated with the combination of the spreading factor, SFD, of four and the chip repetition factor, CRF, of four improves the required average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) for the average packet error rate of 10-2 by approximately 2.0 dB compared to DS-CDMA only employing SFD = 16 assuming four simultaneously accessing users in an exponentially decaying six-path Rayleigh fading channel with two-branch diversity reception.

To support high bit rate and high quality indoor radio communication systems, we have to solve intersymbol interference (ISI) problem caused by frequency-selective fading. Recently multi-carrier modulation technique is considered to be one of the effective methods for this problem. In this paper we propose Partial Frequency ARQ (Automatic Repeat reQuest) system which can achieve effective ARQ scheme for multi-carrier packet communication. This system operates partial retransmission of erroneous power faded packets, and it is superior to the traditional ARQ systems. Furthermore two different protocols are examined for this system: Static Carrier Assignment (SCA) and Dynamic Carrier Assignment (DCA). By computer simulation we found that DCA method can achieve better performance than SCA in terms of both throughput and packet transmission delay.

An efficient ARQ scheme based on the packet combining technique is investigated for multi-carrier modulation systems. In multi-carrier modulation systems, several sub-carriers are used for high data rate transmission and their individual received signal quality becomes different from one sub-carrier to others in a frequency selective fading channel. Therefore by changing the assignment of data to the sub-carriers in the retransmission packets, the distortion between the previous transmitted packet and the newly retransmitted one will be different. This is the principle of the proposed adaptive data order rearrangement for a packet combining ARQ scheme, which can achieve more diversity gain in packet combining and improve the ARQ performance. From the results of the theoretical analysis and the computer simulation, it is confirmed that the proposed packet combining ARQ with the proposed operation can achieve the better performance in terms of the average packet transmission success probability. In addition, this proposed scheme is also compared with the conventional multi-carrier modulation ARQ scheme based on the partial retransmission of a packet. The computer simulation results demonstrate that the proposed scheme has also advantage against the latter one, and it is considered to be as a more efficient ARQ scheme for multi-carrier modulation systems.

This paper proposes an accurate Fast Fourier Transform (FFT) window timing detection method based on the maximum signal-to-interference power ratio (SIR) criterion taking into account the received signal and inter-symbol interference power according to different detected FFT window timings in Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access. In the proposed method, the SIR of the received signal is estimated using the desired signal power and inter-symbol interference power calculated based on the power delay profile, which is measured by the cross-correlation between the pilot symbol replica and the received signal. Furthermore, since the SIR is calculated only for the received path timing of the first path and those paths exceeding the guard interval duration, the computational complexity of the proposed method is low. Computer simulation results show that the proposed scheme reduces the required average received signal energy per symbol-to-noise power spectrum density ratio (Es/N0) for achieving the average packet error rate of 10-2 by approximately 1.0 dB compared to the conventional method, which detects the forward path timing of the power delay profile (16QAM data modulation, six-path Rayleigh fading channel, and the maximum delay time of 3 µsec (root mean squared (r.m.s.) delay spread of 0.86 µsec)).

This paper presents throughput performance along with power profiles in the time and frequency domains over 100 Mbps based on field experiments using the implemented Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) transceiver with a 100-MHz bandwidth in a real multipath fading channel. We conducted field experiments in which a base station (BS) employs a 120-degree sectored beam antenna with the antenna height of 50 m and a van equipped with a mobile station (MS) is driven at the average speed of 30 km/h along measurement courses that are approximately 800 to 1000 m away from the BS, where most of the locations along the courses are under non-line-of-sight conditions. Field experimental results show that, by applying 16QAM data modulation and Turbo coding with the coding rate of R = 1/2 to a shared data channel together with two-branch antenna diversity reception, throughput over 100 and 200 Mbps is achieved when the average received signal-to-interference plus noise power ratio (SINR) is approximately 6.0 and 14.0 dB, respectively in a broadband channel bandwidth where a large number of paths such as more than 20 are observed. Furthermore, the location probability for achieving throughput over 100 and 200 Mbps becomes approximately 90 and 20% in these measurement courses, which experience a large number of paths, when the transmission power of the BS is 10 W with a 120-degree sectored beam transmission.

This paper proposes a pilot channel assisted minimum mean square error (MMSE) combining scheme in orthogonal frequency and code division multiplexing (OFCDM) based on actual signal-to-interference power ratio (SIR) estimation, and investigates the throughput performance in a broadband channel with a near 100-MHz bandwidth. In the proposed MMSE combining scheme, the combining weight of each sub-carrier component is accurately estimated from the channel gain, noise power, and transmission power ratio of all the code-multiplexed channels to the desired one, by exploiting the time-multiplexed common pilot channel in addition to the coded data channel. Simulation results elucidate that the required average received signal energy per bit-to-noise spectrum density ratio (Eb/N0) for the average packet error rate (PER) = 10-2 is improved by 0.6 and 1.2 dB by using the proposed MMSE combining instead of the conventional equal gain combining (EGC) in a 24-path Rayleigh fading channel (exponential decay path model, maximum delay time is approximately 1 µsec) in an isolated cell environment, when the number of multiplexed codes = 8 and 32, respectively, with the spreading factor of 32. Furthermore, when the average received Eb/N0 = 10 dB, the achievable throughput, i.e., the number of simultaneously multiplexed codes for the average PER = 10-2 in the proposed MMSE combining, is increased by approximately 1.3 fold that of the conventional EGC.

This paper investigates the impact of inter-carrier interference (ICI) due to Doppler spread on the packet error rate (PER) performance in Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access employing turbo coding in a multipath fading channel, and describes the optimization of the sub-carrier spacing, Δ f, i.e., the number of sub-carriers, Nc, with an approximate 50-100 MHz bandwidth. Simulation results show that although the uncoded OFCDM in a 1-path flat Rayleigh fading channel is affected by the ICI caused by the Doppler spread when the maximum Doppler frequency, fD, becomes more than 5% of Δ f, OFCDM employing turbo coding in a 24-path Rayleigh fading channel is robust against Doppler spread and the degradation is not apparent until fD reaches more than 10% of Δ f. This is because the turbo coding gain and the frequency diversity effect compensate for the degradation due to ICI. Meanwhile, the PER performance with a larger Nc is degraded, since the effect of the error correction capability becomes smaller due to the larger variance of the despread OFCDM symbols associated with the narrower spreading bandwidth in the frequency domain. Consequently, along with the packet frame efficiency for accommodating the guard interval to compensate for the maximum multipath delay time of 1 µsec, we clarify that the optimum number of sub-carriers is approximately 512-1024 (the corresponding Δ f becomes 156.3-78.1 kHz) for broadband OFCDM packet wireless access assuming a 50-100 MHz bandwidth.

This paper presents an optimum antenna diversity combining method associated with despreading that employs Minimum Mean Square Error (MMSE) combining over the frequency domain in a frequency-selective fading channel for forward link Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access, in order to achieve the maximum radio link capacity. Simulation results considering various propagation channel conditions elucidate that the antenna diversity combining method with Equal Gain Combining (EGC) subsequent to the despreading employing MMSE combining based on pilot symbol-assisted channel estimation and interference power estimation can decrease the required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) the most, taking into account the impact of the inter-code interference. Furthermore, we clarify that the required average received Eb/N0 for the average packet error rate of 10-2 employing the diversity combining scheme with EGC after despreading with MMSE combining is improved by approximately 0.3 dB compared to the diversity combining scheme with EGC before despreading with MMSE combining at the number of code-multiplexing of 24 for the spreading factor of 32 in a 24-path Rayleigh fading channel.

This paper compares the radio link capacity between multi-carrier/DS-CDMA (MC/DS-CDMA) and multi-carrier CDMA (MC-CDMA) for reverse-link broadband packet wireless access taking into consideration: the asynchronous signal reception at the receiver; the path timing or symbol timing detection of all major subject factors; and the channel estimation error. Simulation results show that although the influence of the asynchronous signal reception on the packet error rate (PER) performance in MC-CDMA is slight, the degradation caused by the channel estimation error in MC-CDMA is severe compared to that caused by the path timing detection error in MC/DS-CDMA. Consequently, the required average received signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average PER of 10-2 in MC/DS-CDMA is reduced by approximately 4.5 dB compared to that in MC-CDMA assuming a 12-path exponential decayed Rayleigh fading channel. Furthermore, the number of accommodated users in MC/DS-CDMA is 2.5 fold greater than that in MC-CDMA employing two-branch antenna diversity reception. Therefore, we conclude that MC/DS-CDMA is more appropriate than MC-CDMA for the reverse link broadband packet wireless access, and that it has advantageous features such as an inherently much lower peak-to-average power ratio compared to MC-CDMA, which accompanies a high peak-to-average power ratio causing an increase in the back-off of the power amplifier.

This paper proposes a multipath interference canceller (MPIC) employing multipath interference (MPI) replica generation (MIG) utilizing previously transmitted packet combining (PTPC), which is well-suited to incremental redundancy, in order to achieve a peak throughput of nearly 8 Mbps in a multipath fading environment in high-speed downlink packet access (HSDPA). In our scheme, more accurate MPI replica generation is possible by generating MPI replicas utilizing the soft-decision symbol sequence of the previously transmitted packets in addition to that of the latest transmitted packet. Computer simulation results elucidate that the achievable throughput of the MPIC employing MIG-PTPC is increased by approximately 100 kbps and 200 kbps and the required average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) per antenna at the throughput of 0.8 normalized by the maximum throughput is improved by about 0.3 and 0.7 dB compared to that of the MPIC using the soft-decision symbol sequence after Rake combining of the last transmitted packet both in 2- and 3-path Rayleigh fading channels for QPSK and 16QAM data modulations, respectively. Furthermore, we clarify that the maximum peak throughput using the proposed MPIC with MIG-PTPC coupled with incremental redundancy achieves approximately 7 Mbps and 8 Mbps with 16QAM and 64QAM data modulations in a 2-path Rayleigh fading channel, respectively, within a 5-MHz bandwidth.

This paper proposes the optimum design for adaptively controlling the spreading factor in Orthogonal Frequency and Code Division Multiplexing (OFCDM) with two-dimensional spreading according to the cell configuration, channel load, and propagation channel conditions, assuming the adaptive modulation and channel coding (AMC) scheme employing QPSK and 16QAM data modulation. Furthermore, we propose a two-dimensional orthogonal channelization code assignment scheme to achieve skillfully orthogonal multiplexing of multiple physical channels. We first demonstrate the reduction effect of inter-code interference by the proposed two-dimensional orthogonal channelization code assignment. Then, computer simulation results show that in time domain spreading, the optimum spreading factor, except for an extremely high mobility case such as for the fading maximum Doppler frequency of fD = 1500 Hz, becomes SFTime = 16. Furthermore, it should be decreased to SFTime = 8 for such a very fast fading environment using 16QAM data modulation. We also clarify when the channel load is light such as Cmux/SF = 0.25 (Cmux and SF denote the number of multiplexed codes and total spreading factor, respectively), the required average received signal energy per symbol-to-noise power spectrum density ratio (Es/N0) is reduced as the spreading factor in the frequency domain is increased up to say SFFreq = 32 for QPSK and 16QAM data modulation. When the channel load is close to full such as when Cmux/SF = 0.94, the optimum spreading factor in the frequency domain is SFFreq = 1 for 16QAM data modulation and SFFreq = 1 to 8 for QPSK data modulation according to the delay spread. Consequently, by setting several combinations of spreading factors in the time and frequency domains, the near maximum link capacity is achieved both in cellular and hotspot cell configurations assuming various channel conditions.

This paper presents a performance comparison of the channel-interleaving method in the frequency domain, i.e., bit interleaving after channel encoding, symbol interleaving after data modulation, and chip interleaving after spreading, for Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) wireless access with frequency domain spreading, in order to reduce the required average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) and achieve the maximum radio link capacity. Simulation results show that, for QPSK data modulation employing turbo coding with the channel coding rate R=3/4, the chip-interleaving method decreases the required average received Es/N0 the most for various radio parameters and propagation model conditions, where the number of code-multiplexing, Cmux, the spreading factor, SF, the r.m.s. delay spread, σ, the number of multipaths, L, and the maximum Doppler frequency, fD, are varied as parameters. For example, when Cmux=12 of SF=16, the improvement in the required average received Es/N0 from the case without interleaving at the average packet error rate (PER) of 10-2, is approximately 0.3, 0.3, and 1.4 dB for the bit, symbol, and chip interleaving, respectively, in a L=12-path exponential decayed Rayleigh fading channel with σ of 0.043 µsec and fD of 20 Hz. This is because the chip interleaving obtains a higher diversity gain by replacing the chip assignment over the entire bandwidth. Meanwhile, in 16QAM data modulation with R=1/2, the performance of the chip interleaving is deteriorated, when Cmux/SF>0.25, due to the inter-code interference caused by different fading variations over the spreading duration since the successive chips during the spreading duration are interleaved to the separated sub-carriers. Thus, bit interleaving exhibits the best performance although the difference between bit interleaving and symbol interleaving is slight. Consequently, we conclude that the bit-interleaving method is the best among the three interleaving methods for reducing the required received Es/N0 considering the tradeoff between the randomization effect of burst errors and the mitigation of inter-code interference assuming the application of adaptive modulation and channel coding scheme in OFCDM employing frequency domain spreading.

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 evaluates the downlink performance of an LTE-Advanced (LTE-A) heterogeneous network that uses carrier aggregation (CA) between macro and small cells. The concept of utilizing the CA functionalities in LTE-A is effective in increasing the network capacity in a congested area through raising of the base station density using small cells overlaid onto an existing macro cell network. This concept is also effective in maintaining the mobility performance of user equipment (UE) because handover operation is not applied when entering/leaving a small cell, but component carrier addition/removal is only performed through CA while maintaining the connection to a macro cell. In order to present comprehensive performance evaluations in an LTE-A heterogeneous network with CA, this paper evaluates various performance criteria, e.g., downlink cell throughput and downlink user throughput. According to the obtained simulation results, the total downlink cell throughput achieved in an LTE-A heterogeneous network deployment with CA (four small cells overlaid onto a macro cell sector) exhibits a 3.9-fold improvement compared to a conventional-macro-cell-only network deployment using two frequency bands.

This paper elucidates the optimum bandwidth per sub-carrier in the reverse link for multicarrier (MC)/DS-CDMA using a 10 to 80-MHz bandwidth in a multipath fading channel with numerous resolved multipaths, taking into account all major effects, i.e., the improvement in the Rake time diversity effect and the degradation in the path search and the channel estimation due to multipath interference (MPI). In the paper, we assume a broadband channel model with the maximum delay time of up to approximately 1 µsec simulating a microcell with the radius of less than 1 km in an urban area. The simulation results clarify that the improvement in the radio link performance is almost saturated at a bandwidth greater than approximately 40 MHz when the spreading factor of the channel is SF=32, and the best performance is achieved at the bandwidth of approximately 20-40 MHz when SF=4, employing two-branch antenna diversity reception (an average equal power delay profile and an exponential decay power delay profile are assumed, where the number of multipaths is changed from 12 to 48 for both profiles). This is generated by the tradeoff between the improvement in the Rake time diversity effect and the increased MPI in addition to the degradation in accuracy of the path search and channel estimation associated with a lower average received signal-to-interference plus background noise power ratio. Therefore, we conclude that MC/DS-CDMA, where each sub-carrier has the bandwidth of approximately 20-40 MHz, is one of the most promising candidates for broadband packet wireless access in the reverse link.