Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1999-12-29
2003-08-05
Chin, Stephen (Department: 2734)
Pulse or digital communications
Transceivers
Modems
C375S265000, C375S267000, C375S268000, C375S271000, C375S299000, C375S302000, C708S520000, C708S607000, C708S203000, C714S701000, C714S774000, C714S792000, C714S810000, C455S521000, C455S101000, C455S110000
Reexamination Certificate
active
06603809
ABSTRACT:
The present invention relates generally to the communication of data upon a channel susceptible to fading, such as a radio channel upon which data is transmitted during operation of a cellular communication system. More particularly, the present invention relates to apparatus, and an associated method, by which to increase the transmission diversity of the data communicated upon the channel, thereby to facilitate the recovery of the data once received at a receiving station.
BACKGROUND OF THE INVENTION
The use of wireless communication systems has achieved wide popularity in recent years as a result of advancements in communication technologies. Multi-user, wireless communication systems of improved capabilities are regularly utilized by large numbers of consumers to communicate both voice and nonvoice information.
In a wireless communication system, a communication channel formed between a sending station and a receiving station is a radio channel defined upon a portion of the electromagnetic spectrum. Because a radio channel forms a communication link between the sending and receiving stations, a wireline connection is not required to be formed between the sending and receiving stations to permit the communication of data between the stations. Communication by way of a wireless communication system is thereby permitted at, and between, locations at which the formation of a wireline connection would not be practical. Also, because a communication channel is formed of a radio channel, a radio communication system can be more economically installed as the infrastructure costs associated with a wireline communication system are significantly reduced.
A cellular communication system is exemplary of a wireless, multi-user radio communication system which has achieved wide levels of usage and which has been made possible due to advancements in communication technologies. A cellular communication system is typically formed of a plurality of fixed-site base stations installed throughout a geographical area which are coupled to a PSTN (public-switched, telephonic network). Portable transceivers, typically referred to as mobile stations, mobile terminals, or cellular phones, communicate with the base stations by way of radio links.
A cellular communication system efficiently utilizes the portion of the electromagnetic spectrum allocated thereto. Because of the spaced-apart positioning of the base stations, only relatively low-power signals are required to effectuate communications between a base station and a mobile station. As a result, the same frequencies can be reused at different locations throughout the geographical area. Thereby, communications can be effectuated between more than one set of sending and receiving stations concurrently at separate locations throughout the area encompassed by the cellular communication system.
In an ideal communication system, a communication signal, when received at a receiving station, is substantially identical to the corresponding communication signal when transmitted by a sending station. However, in a non-ideal communication system in which the communication signal must be transmitted upon a non-ideal communication channel, the signal, when received at the receiving station, is dissimilar to the corresponding communication signal when sent by the sending station. Distortion of the communication signal caused by transmission of the communication signal upon the communication channel causes such dissimilarities to result. If the distortion is significant, the informational content of the signal cannot be recovered at the receiving station.
The communication channel might be of characteristics which distort the value of the information bearing bits conveyed by a communication signal. Fading, such as that caused by multi-path transmission, or Raleigh fading, alters the communication signal during its transmission. Such distortion, if not corrected, reduces the communication quality levels in a communication session formed between a sending and receiving station.
Various techniques are utilized to overcome distortion introduced upon a communication signal as a result of transmission upon a non-ideal communication channel.
Time encoding of the communication signal, prior to its transmission, for instance, increases the redundancy of the transmitted signal. By increasing the time redundancy of the signal, the likelihood of the informational content of the signal being recoverable, once received at the receiving station, is increased. Increasing the time redundancy of the signal is sometimes referred to as creating time diversity.
Also, space diversity is sometimes also utilized, for transmission of communication signals. Typically, space diversity refers to the utilization of more than one transmit antenna transducers from which a communication signal is transmitted, thereby to provide spatial redundancy. The two antennas must be separated enough to insure that their signals fade in an uncorrelated fashion. The use of space diversity does not have to be separated from encoding in the time domain. When space and time diversity are used together, the encoding in the time domain should be done jointly, across the different antenna transducers, in order to efficiently combine the two forms of diversity.
Combinations of both space and time coding further enhances transmission diversity to combat signal fading caused by multi-path transmission. t any symbol epoch, exactly one symbol is transmitted from each transmit antenna. Each transmitted symbol is selected from the constellation of signal points that characterizes the modulator associated with a particular antenna. Note that the constellations pertaining to the different transmit antennas can be in general different, but in practice it may be preferable to have identical signal constellations for all transmit antennas. The particular constellation points selected to be sent over the different transmit antennas during an arbitrary (multiple) transmission are appropriately determined from the encoder's output symbols. Trellis encoding is sometimes used to effectuate space time coding. In that case, the selection of the constellation points, starting from the encoder's output symbols, is decided by a construction, referred to as a trellis, which describes all possible transitions between a given, finite number of states. The states are tuples of certain most recent symbols, e.g., bits, applied to the input of the trellis encoder. For example, if the input sequence consists of raw information bits, then the tuples reflect the most recent past history of the information bit sequence which is provided to the trellis encoder, and the trellis describes a transformation of an input sequence of bits, into an output sequence of symbols, referred to as a coded symbol sequence. Note that the coded symbols can be nonbinary, too. The trellis is represented by successive columns, referred to as states, and transitions between states of successive columns are referred to as transitions. Each branch corresponds to a particular combination of new input symbols while in a given state. A mapper is utilized to map each coded symbol to a signal constellation point, thus determining the modulation parameters for a carrier signal.
In construction of the trellis and the mapper, a significant goal is to optimize the manner by which labels to trellis branches are assigned and to optimize the manner by which constellation points are assigned to the symbols used in the trellis branch labels. The optimality of the assignation is characterized in terms of a measure, referred to as a distance between two different codewords. The distance, ultimately, is determinative of the physically-meaningful, probability of a receiving station mistaking one codeword for another. The smaller the probability of a mistake, the better shall be the performance of a space-time code that is utilized in the effectuation of the communication. In-order to ensure as large of a distance as possible between two codewords, a succession of points se
Chin Stephen
Fraccaroli Federico
Ha Dac V.
Nokia Corporation
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