Recent papers have shown that space-time (ST) coding using continuous phase modulation has a number of advantages relative to linear modulation, among which is its constant envelope, which allows transmission with inexpensive and power-efficient Class C amplifiers. The present paper presents a particularly simple variant, ST coding based on minimum shift keying (MSK), an offset format. ST codes with offset modulation give much better performance than quadrature phase shift-keying (QPSK), for the same number of states, and the MSK ST decoding computational load is smaller than that of QPSK by a ratio that improves exponentially with the number of transmitter antennas. The relationship between offset and nonoffset modulation formats is explored and the effect of pulse shape is shown explicitly.

Space-time coding using MSK

Space-time coding has shown great promise for digital transmission in wireless communication links, especially when the channel response is known at the receiver. Space time coding combined with continuous phase modulation (CPM) can offer better tradeoffs in bandwidth and power efficiency. Because of the memory inherent in CPM, channel estimation is often harder than for linear modulations. We present an adaptive soft algorithm that performs joint channel estimation and data detection for space-time CPM systems. Properly designed pilot symbols are inserted at the very beginning to give good initial estimates of the channels. This soft receiver is further applied to the interleaved space-time CPM system to yield better performance with moderate complexity through iterative processing. Simulation results show that the receiver can often achieve near-coherent performance in quasistatic fading as well as in time-varying fading.

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Soft-output demodulator in space-time-coded continuous phase modulation

We derive a novel space-time code (STC) design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space-time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of the combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters.

Space-time code design for CPFSK modulation over frequency-nonselective fading channels

Space-Time codes have shown considerable promise for reliable transmission over wireless fading channels by eeciently employing transmit diversity. Past work only considered design of space-time codes with linear modulation. In this paper we give the design criterion of space-time codes for at Rayleigh Fading channel in CPM system. A simple code example is provided to demonstrate its good performance and then applied to an interleaved trellis-coded space-time CPM (TC-ST-CPM) system. The corresponding adaptive soft-output detection algorithm is also presented.

Space-Time Coding for Rayleigh Fading Channels in CPM system

The Alamouti orthogonal space-time block code for two transmit antennas was designed primarily for QAM and PSK modulations, and we have previously generalized it for the continuous phase modulation (CPM), denoted as OST-CPM, by maintaining the orthogonality (for the fast ML decoding/demodulation) and the phase continuity of two signals from two transmit antennas. In this paper, we design orthogonal-like space-time coded CPM systems for three and four transmit antennas based on orthogonal and quasi-orthogonal space-time codes. Although the signals from transmit antennas in the proposed orthogonal-like space-time coded CPM systems are not orthogonal, the fast decoding/demodulation is maintained like the two transmit antenna case. Simulation results show that the performance of the proposed orthogonal-like space-time coded CPM systems for four transmit antennas is much better than that of the OST-CPM systems for two transmit antennas.

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Orthogonal-Like Space–Time-Coded CPM Systems With Fast Decoding for Three and Four Transmit Antennas

Soft output detection algorithms are useful in systems where soft-decision metrics are important, e.g., systems with interleaved coded modulation. Receive diversity techniques can provide significant performance improvement for fading channels encountered in mobile communication systems. A soft-output receive diversity combining algorithm for the demodulation of continuous phase modulated (CPM) signals over space-time correlated frequency flat Rayleigh fading channels in the absence of perfect channel state information (CSI) is developed. The derived soft output algorithm is used in the iterative detection of interleaved TC-CPM. The performance of the algorithm is extensively characterized by means of Monte-Carlo simulations.

Soft output diversity combining for CPM signals over space-time correlated Rayleigh fading channels

Space-time coding has shown great promise for digital transmission in wireless communication links, especially when the channel response is known at the receiver. Combined with continuous phase modulation (CPM), better bandwidth and power efficiency can be obtained. But without the perfect channel state information, the high performance of space-time CPM system can be greatly degraded due to the channel estimation errors. In this paper we present an adaptive soft algorithm which performs joint channel estimation and data detection for space-time CPM system. Properly designed pilot symbols are inserted at the very beginning to give a good initial estimate of the channels. This soft demodulator is further applied to the interleaved space-time CPM system to yield better performance with moderate complexity. Simulation results show that the receiver can often achieve near-coherent performance in quasi-static fading as well as in relatively fast fading.

Xiaoxia Zhang

Papers

Space-Time Coding for Rayleigh Fading Channels in CPM system

Soft output diversity combining for CPM signals over space-time correlated Rayleigh fading channels

An adaptive soft-output receiver in space-time coding with continuous phase modulation