On the design of multiple antenna systems with continuous phase modulation

Continuous phase modulation (CPM) has been an attractive modulation scheme for digital transmission over both powerand bandwidth-limited channels such as in mobile satellite communications. CPM signals have a constant envelope so that low-cost nonlin­ ear amplifier can be used to achieve power efficiency. Meanwhile, it can be designed to yield good spectral properties with the maintained phase continuity. Its advantage over lin­ ear modulation will be demonstrated by the simulated symmetric information rate in this dissertation. As we know, unlike Gaussian channel, the wireless channel suffers from fading caused by multipath and movement in the radio links. The severe attenuation induced through fading makes it impossible for the receiver to determine the transmitted signal unless some diversity resources are used. Space-time coding can take advantage of the space diversity introduced by multiple transmit antennas in addition to the time diversity. Combined with CPM (ST-CPM), it can achieve better bandwidth and power efficiency. One of the challenges in space-time code design with CPM is to guarantee full spatial diversity due to both the nonlinearity of the modulation and the more complex resulting performance metrics. We developed some systematic design theorems to ensure full diver­ sity with certain CPM schemes in quasi-static fading based on the linear decomposition and binary rank criteria available in linear modulation. With these theorems, the design of full spatial diversity space-time codes can be greatly simplified. Furthermore, we can make use ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the traditional error correcting codes for single antenna system which have been studied for a long time and transform some of them to space-time codes. With large Euclidean distances and guaranteed space diversity, these codes can often provide high performance. However, most space-time codes are constructed under the assumption that transmit­ ter does not know the channel but the perfect channel state information (CSI) is available at the receiver. Perfect channel estimation in space-time coding can be quite challenging due to lots of path gains involved. In the presence of channel estimation errors, a perfor­ mance degradation has to be expected, especially in the time-varying channels. We derive the joint channel estimation and data detection where the fixed-lag maximum a posteriori « probability is calculated and the CSI is implicitly estimated through a linear Wiener predic­ tion filter. With properly designed pilot symbols, this algorithm can provide near-coherent performance both in quasi-static fading and in time-varying fading. The complexity of the optimal decoding of ST-CPM is quite prohibitive with complex space-time code even when the receiver knows channel perfectly, not to mention when the channel needs to be estimated. We propose the interleaved system by concatenating a sim­ ple ST-CPM with outer code through a random interleaver. This serial concatenated system can achieve high performance with moderate overall complexity by iterative decoding. The performance gain is even more significant in relatively fast fading since time diversity can be exploited. Although CPM system has significant advantage for its low power, low cost trans­ mitter, the relatively lower bandwidth efficiency has precluded its widespread use due to the inability to use amplitude to communicate information. Since the multiple antenna (MIMO) system can establish high rate communications by implementing many low rate parallel channels, with the increased symmetric information rate, using CPM in a MIMO