A system is proposed and analyzed, which uses several transmit antennas to achieve diversity in a flat fading mobile radio environment. The signals at different antennas carry the same digital information, but have different modulation parameters (modulation diversity). In contrast to other proposals, no bandwidth expansion is required. Modulation diversity for quadrature amplitude modulation (QAM) type modulation is achieved by using different partial response type base pulses. Simulation results confirm the expected gain. >

A new bandwidth efficient transmit antenna modulation diversity scheme for linear digital modulation

A base station modulation diversity scheme is proposed for simulcast systems which use linear QAM (quadrature amplitude modulation) type modulation. With this method the bandwidth efficiency is fully preserved because each base station uses the same base pulse. Modulation diversity is achieved by filtering the input symbols with a symbol-spaced finite impulse response (FIR) filter prior to QAM modulation. The tap weights of the FIR filters at different base stations are different. They are chosen such that a necessary condition for optimum diversity gain in time-selective fading is satisfied. Examples for simulcast with two base stations are given. They demonstrate the impact of the choice of tap weights on the energy efficiency, the system complexity, and the performance in the presence of a propagation delay difference between the signals of different base stations. >

Basestation modulation diversity for digital simulcast

A novel transmitter diversity scheme that generates forced fading to improve the performance of channel coding is proposed and investigated. Since the required phase sweeping frequency is much smaller than the transmission bit rate, bandwidth expansion is negligible. A sinusoidal phase sweeping function Delta Theta sin(2 pi f/sub H/t) is employed in laboratory experiments using 32 kbit/s quarternary differential phase shift keying (QDPSK) with differential detection and BCH(23,12) code. It is shown that Delta Theta =200 degrees and f/sub H/=67 Hz can be used when m (interleaving depth)=10 b. Hence, excessively long interleaving is not required by the use of transmitter diversity. Under very slow Rayleigh fading (f/sub D/=1 Hz), a measured improvement of 4.8 dB is obtained at a word error rate of 10/sup -2/ without receiver diversity. Applications include paging systems that require very simple receivers. >

Combined effects of phase sweeping transmitter diversity and channel coding

In a radiotelephone system, the control channel in all cells in an area can be simulcasted A microcell base station may be provided with a receiver to listen on the umbrella cell control channel for messages, in addition to listening on its own control channel for control information and call accesses, to facilitate the appropriate assignment of a call to a cell Also, a microcell can share a control channel with an umbrella cell provided interference between the control channels is not excessive Further, microcells can share a common control channel independent of the overlying macrocell structure

Communication management technique for a radiotelephone system including microcells

Coded modulation (usually with interleaving) is used in fading channel communications to achieve a good error performance. The major benefit from using coded modulation in fading channels is achieved if each code symbol of a codeword (or coded sequence) suffers statistically different fading (preferably independent fading). However, in many applications of mobile communications (e.g., in a metropolitan environment), a low vehicle speed (and hence, a small Doppler spread, f/sub D/) is very common. With a small Doppler spread, ideal or close-to-ideal interleaving is no longer feasible and all code symbols of a codeword would suffer highly correlated fading especially in stationary fading (f/sub D//spl ap/0). Coded modulations will thus suffer seriously degraded performance. Previous performance analyses based on ideal interleaving are not accurate when a small Doppler spread is encountered and the much used union bound error probability analysis is loose for small Doppler spreads. To rectify this situation, this paper presents an improved performance analysis of coded modulations with correlated fading and pilot-symbol-assisted modulation (PSAM). Transmitter diversity can generate the necessary time-varying fading to maintain the effectiveness of a coded signaling scheme which this paper examines in detail using an intentional frequency offset between antennas. This work found that proper selections of the intentional frequency offset and interleaving depth can lead to good performance with traditional coded modulations (if enough antennas are used) using essentially the same simple demodulation structure as used in the traditional single-antenna PSAM.

/pdf/design-and-analysis-of-transmitter-diversity-using-5beqbkg0s0.pdf

Design and analysis of transmitter diversity using intentional frequency offset for wireless communications

Many mobile radio communication systems require digital signaling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. A new modulation scheme intended to realize simulcast digital transmission is described. In this method, a modulation signal is made by superimposing a specific wave on an ordinary rectangular digital wave. The two conditions necessary for obtaining a diversity effect equivalent to the maximal-ratio combining are mathematically derived. The specific waves for the various transmitters may be sinusoidal waves having a frequency equal to the original bit rate, and phases which differ from one transmitter to another. In order to clarify the feasibility of this technique, experimental simulation tests have been performed in the 900-MHz band in a two-transmitter configuration. It is proved that this modulation scheme, in comparison with the carrier-frequency offset strategy, not only gives the same amount of improvement in digital signaling in an overlapped area, but also makes the allowable carrier frequency drift more than ten times larger.

http://ieeexplore.ieee.org/iel5/25/34047/01622763.pdf

A new modulation scheme for multitransmitter simulcast digital mobile radio communication

Many mobile radio communication systems require digital siganling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. This paper describes a new modulation scheme in order to realize a simulcast digital transmission. In this method modulation signal is made by superimposing a sinusoidal wave on an ordinary rectangular digital wave. When Manchester-coded type signal is used, the frequency of the sinusoidal wave is twice as much as that of the original bit-rate and the relative phase difference between the two waves is different at each base station. In order to clarify the feasibility of this technique, experimental simulation tests are performed on 900-MHz band in two transmitter construction. It is proved that this modulation scheme does not only give the same amount of the improvement effect on the digital signaling on an overlapped area, but also makes the allowable carrier frequency drift several times lager than that of the carrier frequency offset strategy.

http://ieeexplore.ieee.org/iel5/10798/34045/01622669.pdf

S. Ogose

Papers

A new modulation scheme for multitransmitter simulcast digital mobile radio communication

A new modulation scheme for multitransmitter simulcast digital mobile radio communication