Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1997-05-05
2001-01-09
Pham, Chi H. (Department: 2731)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C375S347000, C455S277200
Reexamination Certificate
active
06172970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an antenna diversity receiver for radio communication systems, and more particularly to a low-complexity antenna diversity receiver having implemented on a single receiver unit a plurality of inter-switchable diversity schemes. Furthermore, this invention relates particularly to an antenna diversity receiver especially suitable for use as a portable handset for Personal Communication Systems (PCS), such as Time Domain Multiple Access (TDMA) Communication Systems.
BACKGROUND OF THE INVENTION
It is well known that antenna diversity can improve the reception quality of communications in a wireless environment and yield increased system capacity. Conventionally, selection diversity is the simplest diversity scheme which operates on the principle of selecting the antenna diversity branch which provides the strongest received signal level or the best eye-opening. However, it is known that selection diversity does not provide any useful gain in a line-of-sight (LOS) environment since the two branches are correlated.
In a recent paper by Cox and Wong, “Low-Complexity Diversity Combining Algorithm and Circuit Architectures for Co-channel Interference Cancellation and Frequency Selective Fading Mitigation”,
IEEE Trans. Comm. Vol,
44, no 9, pp. 1107-1116, September 1996, it is shown that two antenna optimum-combining diversity produces a signal-to-interference ratio (SIR) improvement of at least 3-dB over conventional two-antenna selection diversity in Personal Access Communication Systems (PACS). This is attractive since combining diversity can be applied to cancel co-channel interference and boost the desired signal even in an LOS environment.
Qualitatively speaking, in an LOS environment, an optimum-combining receiver adjusts the joint signal of a plurality of antennas, resulting in an adaptive joint antenna pattern or polarization which attenuates co-channel interference while amplifying the desired signal. In a multi-path environment, the antennas may be receiving signals from separate paths and this picture is not entirely applicable, but the concept is the same.
While optimum-combining diversity offers attractive performance improvement over selection diversity, it is noticed that existing antenna diversity researches concentrate on selection diversity. Such a preference is probably due to that fact that many of the so-called adaptive antenna array solutions rely on algorithms which require well characterised antenna patterns. In contrast, most mobile PCS handset antennas possess patterns which are not carefully controlled and are quite dependent on the position of the antenna with respect to the user's hand and head. Thus, if optimum-combining diversity is to be devised and implemented on mobile PCS receiver handsets, the first task would be to seek optimum-combining diversity algorithms which do not require well characterised antennas as a prerequisite.
Hitherto, system complexity together with the associated power consumption, cost and size has been a significant barrier to the wide-spread commercial implementation of diversity schemes in PCS portable handsets since most proposed diversity handset schemes require one receiver chain for each branch of diversity which means that receiver circuitry from RF to baseband has to be duplicated. This dual receiver chain design approach is contradictory to the industrial trend of circuit simplification and consumer appetite of miniaturisation and cost reduction. This limitation, unless circumvented, would continue to hinder implementation and further development of diversity schemes in mobile handsets.
In the Cox & Wong publication above, there is shown a symbolic diagram, i.e.
FIG. 1
, which discloses the concept of a simplified ideal diversity receiver design in which the RF signal from two antenna branches are combined after level adjustment but before further processing presumably by a single channel device for baseband processing. However, this disclosure merely shows a future receiver topology hopefully to be implemented but the underlying algorithm proposed in that publication does not actually support implementation of a diversity receiver using single channel baseband signal processing.
Furthermore, while selection diversity algorithm does not offer significant signal quality improvement in the circumstances mentioned above, it is nevertheless very fast and energy efficient. In circumstances where the signal quality received by one of the antennas is superbly high, selection diversity would be beneficial and it would be highly desirable that the simpler selection diversity can be chosen and utilised. Thus, it would be highly desirable if a diversity receiver handset can accommodate a number of modes of diversity algorithms which can be chosen according to the reception conditions. This would of course require the presupposition that the prime constraints of low-cost, low-complexity and low-weight are observed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a low-complexity antenna diversity receiver design consistent with the prime design constraints, i.e. low-cost, low-complexity and low-weight, which is particularly suitable for handset implementation in PCS. To be implemented as a practical and sophisticated mobile PCS handset, it would be appreciated that the design has to meet the following practical design constraints:—
Firstly, the design should utilise only a single receiver chain and baseband combining processor together with standard baseband processing techniques.
Secondly, the only additional RF frontend components required are low-cost passive components for combining RF signals received through a plurality of antenna branches at the RF front-end.
Thirdly, the system is sufficiently robust to handle poorly-defined, user dependent antenna patterns.
Fourthly, the system is capable of providing several modes of diversity algorithm on single receiver without physically changing the hardware or baseband processing, and can choose the most appropriate diversity mode given the mobile usage and signal environment. For convenience, such a receiver would be referred hereinafter to as “multi-diversity receiver”.
Finally, the techniques can be applied to an increased number of antennas, though at the cost of decreased mobility and lower tolerance to fading.
According to the present invention, there is therefore provided A portable receiver for time division multiplexing access (TDMA) personal communication systems in which a wanted signal burst and a plurality of unwanted signal bursts are transmitted in a time-multiplexed manner within the same signal frame comprising first and second antenna diversity branches, signal combining means and signal processing means, wherein each said antenna diversity branch comprises a low-noise amplifier and means for signal amplitude variation and one of said diversity branches comprises phase shifting means; said signal combining means is adapted to combine the signal outputs from said first and second diversity branches before said signal outputs have undergone any frequency conversion, and said signal processing means is adapted to process the signal output from said signal combining means.
Preferably, the receiver further comprises controlling means, wherein said controlling means is adapted to control said means for signal amplitude variation and said means for adjusting phase shift, the amount of amplitude to be varied and the phase to be shifted being dependent on the signal quality (SQ) of unwanted signal bursts which were respectively received by said first and second diversity branches.
Preferably, said signal quality is a factor indicating the eye-opening of the received unwanted signal bursts and is preferably determined by using a square-law symbol timing
Preferably, wherein said receiver comprises means to select a diversity scheme among a plurality of diversity schemes comprising selection diversity (SD), equal-gain combining (EGC) and interference-reduction combining (IRC) a
Chuang Justin C-I.
Chunning Zhang
Ling Curtis Chih-Shan
Burns Doane Swecker & Mathis L.L.P.
Nguyen Steven
Pham Chi H.
The Hong Kong University of Science and Technology
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