Research On Key Techniques About M-ary Spread Spectrum And Realization Of IC

With the rapid development of communications IC and continious promotion of SOC technology, communications equipment manufacturers tend to realize by IC, from the previous discrete components to the SOC development. Spread Spectrum Communication plays an important role in the communications field. IC design of Spread Spectrum Communication has mainly applied to direct sequence spread spectrum. The M-ary spread spectrum is one most important component in spread spectrum communication system while its IC chip achieves little. The basic theory of M-ary spread spectrum is studied deeply in the paper, which is useful in.the realization of M-ary spread spectrum IC design. Some improved algolithms are given, which suit IC design. And SOC technology is adopted in realization of M-ary spread spectrum chip. The main contribution of paper is as follows:Firstly, two improved scheme combining code polarity of spreading code with code phase of spreading code are proposed for M-ary spread spectrum system which needs synchronization code. Scheme 1 adopts BPSK modulation based on polarity modulation of PN in in-phase branch, and CPSK(code phase shift keying) modulation based on phase modulation of PN code in orthogonal branch. The scheme is easy to realize because all spread spectrum codes comes from one SS code and its reverse order sequence. Compared to the M-ary spread spectrum system which need synchronization code, the new scheme can add a bit of information transmission capacity. Scheme II reduces the resource of spreading code further. In the scheme, the code set of SS codes comes from one SS code by cyclic shifting with the limit of phase area, which is easy for IC design.Secondly, in order to improve the utilization of spreading code resource under the conditions of high bandwidth efficiency, a scheme is proposed which adopts M-ary biorthogonal spread spectrum modulation in in-phase branch, and CPSK spread spectrum modulation in orthogonal branch. The system has the advantages which can achieve synchronization accurately and fleetly by itself, but rather offer additional synchronization resource. The scheme maintains a comparable performance as the M-ary spread spectrum but needs only about quarter of spread spectrum codes of M-ary spread spectrum system, which saves source of spread spectrum codes effectively. And more, an improved scheme is proposed to solve the limitation that conventional spread sptrum communication suffers from spreading code sources. The scheme proposed double code phase shift keying spread spectrum communication system which adopts structure of synchronization frame. The all SS codes come from one SS code by cyclic shifting. Synchronization is achieved by transmit the synchronization code at both orthogonal channels at the same time which is easy to distinguish. Both of the schemes has low complexity and is easy for IC design.Thirdly, in order to improve the bit error ratio(BER) performance of M-ary spread spectrum in fading channel. We propose a scheme which adopts space-time coding before M-ary spread spectrum. And more, we propose applies space time block coding to chips of spread spectrum code which has shorter decoding delay because both detection and decoding can be completely performed within one symbol period. And under the time selective channel, the scheme can get more time diversity, which can improve BER performance.Fourthly, for time selective fast fading condition which is difficult to estimation channel state information, we propose a scheme in which difference space time coding is applied to chips of direct sequence spread spectrum. The scheme is robustness in the presence of oscillator frequency offsets and fast time-selective fading channels. Further more, we apply difference space time coding to chips of M-ary spread spectrum. Compared to the scheme that difference space time coding is applied to chips of direct sequence spread spectrum, the scheme can improve the system performance and information bit rate greatly with the increase of the diversity order. Both the schemes are simple for IC design and acceptable in applications where very low device size and cost are paramount and high speed conditions.Finally, Spread Spectrum System for M-ary core module function is divided, chip-based algorithms are given, IP soft core design and verification are implemented by EDA tools, and digital layout design is also implemented.