This paper proposes Coherent-HYBrid Direct-Sequence Fast-Frequency-Hopping (CHYB-DS-FFH) CDMA with Adaptive Interference Cancelling (AIC) for cellular mobile communications. The features of CHYB-DS-FFH are symbol-by-symbol frequency diversity and low chip-rate DS multiplexing both of which are based on a coherent FFH modulation and demodulation scheme. The combination of coherent FFH, space diversity, and AIC is very effective for reducing the performance degradation due to interference. Computer simulations demonstrate BER performance of a 2 hop 500-kHz-interval frequency hopping system using () a linear canceller or () a nonlinear canceller. Both systems employ the two branch space diversity reception of 10kb/s QPSK with FFH over a 1MHz system bandwidth. In quasi-static channels, the average BER performance is 10-2 with average Eb/N0 less than 8dB. In dynamic fading channels under full interference conditions, CHYB-DS-FFH with the linear adaptive interference canceller realizes a BER of 10-2 at the average Eb/N0 of 15dB with maximum Doppler frequency fD of 5Hz, whereas CHYB-DS-FFH with the non-linear adaptive interference canceller achieves the same BER at the average Eb/N0 of 15dB with fD, equal to 30Hz.

This paper proposes a new signal peak power reduction technique, Peak Reduction based on Control Signal Insertion (PRCSI), for broadband mobile communications based on multi-channel signaling schemes. PRCSI reduces the peak power with a peak control signal that is generated symbol-by-symbol; no signal band expansion is incurred because the peak control signal is inserted into the transmission signal band. PRCSI can achieve 4 dB peak power reduction for 8-carrier signaling, while the Eb/N0 value required to achieve 10-3 average BER is 1 dB larger with PRCSI than without it. This BER performance degradation can effectively be compensated by the proper use of Trellis coding. The proposed technique is applied to OFDM transmission systems with large carrier number. The proposed technique can achieve 3-dB peak power ratio for 128-carrier OFDM signals with less than 1-dB performance degradation at the BER of 10-3.

One of the key technologies to realize future broadband mobile communications is orthogonal frequency division multiplexing (OFDM) transmission. However, the peak-to-average power ratio (PAPR) in OFDM transmission is so much larger than that in single carrier transmission that its adoption in mobile communication systems is uncertain. This paper evaluates the transmission performance possible with iterative peak reduction to design more efficient OFDM transmitters. The PAPR reduction effect and bit error rate (BER) performance are clarified by computer simulations. We calculate the set PAPR value that achieves a target PAPR in the iterative peak reduction method. The required Eb/N0 performance is evaluated under the calculated PAPR condition. The results are effective in designing the back-off value of a transmission power amplifier given fixed transmission quality and computational complexity.

This paper proposes a beam and null simultaneous steering Space-Time Equalizer (S/T-Equalizer). The proposed S/T-Equalizer performs separated S/T-signal processing in order to reduce computational complexity to a practical level. For spatial signal processing, a new Adaptive Array Antenna algorithm is used that combines the beam and null steering concepts. For temporal signal processing, a conventional delayed decision feedback sequence estimation equalizer may be used. The proposed S/T-Equalizer was prototyped, and a series of field tests was conducted using a 5 GHz frequency band to evaluate transmission performances of the proposed system. Results show that the proposed S/T-Equalizer can reduce inter-symbol interference effects while maintaining reasonable signal strength, thereby improving BER performance.

Providing results of a series of link-level simulations for a class of spatial and temporal equalizer (S/T-equalizer) is the primary objective of this letter, which is supplemental to this letter's companion article. The S/T-equalizers discussed in this letter have a configuration that can be expressed as the cascaded connection of adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of the channel delay profile. Both the desired and interference signals suffer from severe inter-symbol interference (ISI). A major difference of this article from its companion letter is that account is taken of the presence of co-channel interference (CCI). Bit error rate (BER) performance of the S/T-equalizer is presented as a result of the link-level simulations that use field measurement data.

This paper proposes an iterative peak power reduction method with adaptive intermediary over-sampling which uses the necessary minimum bandwidth according to iteration number for wireless OFDMA systems. The required bandwidth to each iteration number is evaluated by computer simulation, and over-sampling numbers in iterative processing are controlled by using the simulation results. The results show that the required bandwidth is 1.6, 2.0, and 2.7 times of the used signal bandwidth at the iteration number of 1, 2, and 3, respectively. The proposed adaptive over-sampling method can reduce its multiplication number by 13%.

The large PAPR of orthogonal frequency division multiplexing (OFDM) transmission is one of the serious problems for mobile communications that require severe power saving. Iterative clipping and filtering is an effective method for the PAPR reduction of OFDM signals. This paper evaluates PAPR reduction effect with a graded band-limiting filter in the iterative clipping and filtering method. The evaluation result by computer simulation shows that the excellent peak reduction effect can be obtained in the fewer iteration numbers by using a roll-off filter instead of the conventional rectangular filter, and the iteration number with the roll-off filter achieving the same PAPR is fewer by twice. The result confirms that the clipping and filtering method by using a graded band-limiting filter can achieve low peak OFDM transmission with less computational complexity.

This letter shows the results of a series of link level simulations conducted to evaluate the performances of spatial and temporal equalizers (S/T-equalizers) using field measurement data. The configuration of the spatial and temporal equalizer discussed in this letter can be expressed as a cascade of an adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of channel delay profile. Bit error rate (BER) performances of the S/T-equalizers are presented, and performance sensitivity to symbol timing offset is investigated.

Future broadband mobile communication systems are necessary to achieve the bit rates of 100 Mbit/s. Orthogonal Frequency Division Multiplexing (OFDM) transmission is an attractive technology because it can remove the influence of frequency selective fading in broadband transmission by adding a suitable guard interval to each OFDM symbol. However, peak-to-average power ratio (PAPR) is very large in OFDM transmission. In this paper, we propose a new PAPR reduction method which can be applied even when unusable bands are inside the system band. In the proposed method, peak reduction signals are generated by iterative signal processing only in the usable frequency band, and filtering to remove out-of-band components of the peak reduction signals is incorporated into the iterative signal processing. The results of computer simulation show that the proposed method can effectively reduce peak power without expanding the spectrum both outside the system band and into unusable bands inside the system band. By using the proposed method, the broadband mobile communication system with low peak power and high flexibility of frequency band use can be realized.

This paper aims to improve the performance of the soft canceller followed by simplified minimum mean-square error (SC/S-MMSE) turbo receiver for multiple-input and multiple-output space-division multiplexing/orthogonal frequency division multiplexing (MIMO-SDM/OFDM) transmission; it performs iterative parallel soft interference cancellation and MMSE filtering, and stream-wise soft-input and soft-output decoding. For this aim, we newly introduce two detection techniques: 1) serial interference cancellation, and 2) cyclic redundancy check (CRC)-assisted interference cancellation and MMSE filter tap computation. Various computer simulations are conducted to evaluate the performance enhancement obtained via the use of the two detection techniques. The computer simulation results show that this paper's proposed serial SC/S-MMSE turbo receiver with CRC achieves frame error rate (FER) performance gain over existing MIMO receivers (MMSE receiver, V-BLAST receiver, parallel SC/MMSE-matched filter (MF) turbo receiver, and parallel SC/S-MMSE turbo receiver) for QPSK, 16QAM and 64QAM modulation while keeping the comparable complexity order.