Tatsunori Obara

A Dynamic Channel Assignment Scheme for Distributed Antenna Networks

In this paper, we propose a dynamic channel assignment (DCA) scheme for distributed antenna networks (DANs). DANs, in which many antennas are distributed in each cell, significantly reduce the transmit power compared to conventional cellular networks (CNs). In DAN, a different group of channels should be assigned for each distributed antenna to avoid the interference. Since DAN can also reduce the interference power due to its low transmit power property, the same channel groups can be reused even within the same cell. Proposed DCA scheme dynamically assigns the channels based on the co-channel interference measurement. Computer simulation results demonstrate that the DAN using proposed DCA achieves higher spectrum efficiency than the conventional CN.

Performance analysis of single-carrier overlap FDE

In the single-carrier (SC) transmission, minimum mean square error frequency-domain equalization (MMSE-FDE) can achieve a good bit error rate (BER) performance in a frequency-selective fading channel. The conventional FDE requires the insertion of cyclic prefix (CP) to make the received signal block to be a circular convolution of the transmit signal and the channel. Overlap FDE requires no CP insertion. However, its BER performance improvement is limited by the residual inter-block interference (IBI). In this paper, we present the theoretical analysis of the BER performance achievable with overlap FDE by taking into account the residual IBI after overlap FDE. Then, by using the Gaussian approximation of the residual IBI as well as the residual inter-symbol interference (ISI), we derive the conditional BER for the given set of the channel gains. The average BER performance is numerically evaluated.

Performance of pilot-assisted channel estimation without feedback for broadband ANC systems using OFDM access

AbstractRecently, broadband analog network coding (ANC) has intensively been studied due to its potential to increase the network capacity by exploiting the broadcasting nature of the wireless channel. However, channel state information (CSI) knowledge is required for self-information removal and signal detection. A low-complexity pilot-assisted channel estimation (PACE) scheme has been presented for broadband ANC, where feedback of the CSI estimates from the relay to the users is required. In this study, we propose a PACE scheme without CSI feedback from the relay for broadband ANC using orthogonal frequency-division multiplexing. In the first time slot the users transmit their respective pilots to the relay and in the second time slot the relay simply amplifies and forwards the received pilot signals to both users. Each user can then estimate all the CSI it needs for self-information removal and coherent signal detection, without requiring any feedback of the CSI estimates from the relay. We theoretically analyze the channel estimator’s mean square error (MSE) performance and evaluate the bit error rate (BER) and throughput performance of broadband ANC using the proposed PACE by computer simulation. The results show that the increase in the MSE of the proposed CE scheme causes only a slight BER performance degradation compared to the conventional PACE scheme with ideal feedback. However, the benefit of eliminating the CSI feedback can be seen in the throughput performance.

Joint Transmit/Receive MMSE-FDE for MIMO Analog Network Coding in Single-Carrier Bi-Directional Relay Communications

In this paper, we propose a joint transmit/receive frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion for multi-input multi-output (MIMO) analog network coding (ANC) in single-carrier (SC) bi-directional relay communications. In the proposed scheme, the relay station (RS) equipped with multiple antennas carries out antenna diversity and one-tap transmit FDE, and the base station (BS) and mobile terminal (MT) receivers, both equipped with single antenna, carry out one-tap receive FDE only. The FDE weights at RS, BS and MT are jointly optimized so as to minimize the end-to-end mean square error (MSE). We evaluate, by computer simulations, the bit error rate (BER) performance when using the proposed scheme, and discuss how the transmit FDE at RS operates and affects the BER performance.

Performance evaluation of Low-PAPR transmit filter for single-carrier transmission

Single-carrier transmission is a promising transmission technique due to its low peak-to-average power ratio (PAPR) property compared to multicarrier transmission, and using frequency-domain equalization (FDE) at the receiving side also mitigate the adverse effect of channel frequency-selectivity. An introduction of transmit filter can improve the system performance in terms of either PAPR or error probability. In this paper, we focus on the transmit filter aiming to reduce PAPR by employing the minimization of variance of instantaneous transmit power. Filter roll-off factor is also considered in order to provide excess-bandwidth transmission. With a combination of an FDE and spectrum combining at the receiver, excess-bandwidth transmission inherits additional frequency diversity gain, and therefore improves error probability. Performance evaluation of the proposed filtering algorithm is done by computer simulation, while the PAPR and bit-error rate (BER) performance of proposed algorithm are compared with conventional square-root Nyquist filter.

Selective mapping for broadband single-carrier transmission using joint Tx/Rx MMSE-FDE

Joint transmit/receive frequency-domain equalization based on minimum mean-square error criterion (joint Tx/Rx MMSE-FDE) is a promising frequency-domain-based technique suppressing inter-symbol interference (ISI) in broadband single-carrier (SC) transmission. However, it changes the frequency-domain spectrum shape and hence increases the peak-to-average power ratio (PAPR) of transmit signal. In this paper, we introduce the selective mapping (SLM), which is typically used in orthogonal frequency division multiplexing (OFDM), to reduce PAPR of SC transmission using joint Tx/Rx MMSE-FDE. The SLM is applied to the frequency-domain SC signal after applying the transmit FDE (Tx-FDE) and prior to inverse fast Fourier transform (IFFT). It is shown, by computer simulation, that the SLM can reduce PAPR without significant effect on bit-error rate (BER). Performance of SLM is also evaluated in various phase-rotation sequence types, in both deterministic and random points of views, and number of candidates. Computational complexity of the proposed transmission scheme employing SLM algorithm is also discussed.

Frequency-domain single-carrier spread spectrum with joint FDE and spectrum combining

In this paper, a DFT-based frequency-domain spread spectrum (FDSS) technique for SC transmission is introduced. The transmitted data is initially transformed to frequency-domain signal by using DFT. Frequency-domain spreading can achieve large frequency diversity gain through joint frequency-domain equalization (FDE) and spectrum combining. Performance of the proposed FDSS is evaluated by computer simulation in aspects of bit-error rate (BER), peak-to-average power ratio (PAPR), and average throughput, and then compared to the conventional TDSS scheme with spreading sequence.

Downlink Throughput Performance of Distributed Antenna Network Using Transmit/Receive Diversity

In this paper, we investigate how a distributed antenna network (DAN) offers better throughput performance than a conventional cellular network (CN). In DAN, a group of multiple antennas are distributed in each cell of the CN in order to mitigate the adverse effect of path loss. Moreover, antenna diversity technique can make use of shadowing and multipath fading to improve the transmission performance due to a large spatial diversity gain. In this paper, we consider frequency-domain space-time block coded-joint transmit/ receive diversity (FD-STBC-JTRD) for downlink transmission of single-carrier (SC) DAN. FD-STBC-JTRD uses frequency-domain pre-equalization (pre-FDE) instead of receive FDE to keep the mobile terminals complexity low, and achieves the full-diversity gain. We show by computer simulation that the transmit power for achieving the required throughput can be significantly reduced compared to the conventional CN.

Capacity-Fairness Controllable Scheduling for Uplink Single-Carrier FDMA

The well-known scheduling algorithms are Max-map, Max-Min, and Proportional fairness (PF)-map. Using the above scheduling algorithms, the capacity and the fairness among users vary according to the channel variation. Flexible system design is possible if the sum capacity and the fairness can be controllable. In this paper, assuming single-carrier frequency division multiple access (SC-FDMA) uplink, to control the trade-off between the capacity and the fairness among users, we present modified Max-map, Max-Min, and PF-map. We evaluate, by computer simulation, the sum capacity, the user capacity, and the fairness among users when using the modified scheduling algorithms. It is shown that the modified scheduling algorithms can control the trade-off relationship between the capacity and the fairness among users by changing the number of simultaneously accessing users.

Capacity and BER performance considerations on single-carrier frequency-domain equalization

Single-carrier (SC) waveform has a lower peak-to-average power ratio than multi-carrier waveform. Furthermore, it can exploit the channel frequency-selectivity through frequency-domain equalization (FDE) to improve the transmission performance. SC-FDE is a block transmission. The cyclic prefix (CP) is inserted in front of each data block. Instead of CP insertion, the known training sequence (TS) insertion and zero padding (ZP) can be used. In this paper, performance comparison is made among CP-, TS-, and ZP-SC in terms of the channel capacity and average bit error rate (BER) performance in a frequency-selective Rayleigh fading channel.