Pulse or digital communications – Multilevel
Reexamination Certificate
1998-12-29
2003-05-20
Vo, Don N. (Department: 2631)
Pulse or digital communications
Multilevel
Reexamination Certificate
active
06567475
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the transmission and reception of digital data over radio links, and more particularly, to the transmission and reception of 4-level and 8-level signaling symbols according to prevailing conditions so as to achieve a greater data rate when conditions allow.
BACKGROUND OF THE INVENTION
In a typical cellular telephone system, speech compression is used in order to accommodate as many mobile users as possible within the spectrum allocated to any particular operator. Speech compression involves a tradeoff between the total number of users that can be served by the system, and the speech quality delivered by the system. Where less speech compression is used, a better speech quality is achieved; however, less users can be served by the system. Where a greater amount of speech compression is used, the total number of users that can be served by a system is increased; however, the speech quality is degraded. Similarly, there is a tradeoff between the quality of a data communication service and the number of users that can be accommodated by the service. The quality of a data service may be measured in terms of the time required to transfer a data file. Thus, using a higher bit rate may succeed in completing data transfer faster, thereby leading to increased quality of data communications; however, other users are then prevented from using the spectrum at the same time. Additionally, the number of users that can be accommodated in the spectrum may be increased; however, the quality of data communications is degraded. Thus, an improved system would be one which is able to use less speech compression or use a higher bit rate to transmit data, without reducing the number of users that can be accommodated by the system.
Further, in a cellular telephone system, a transmitted signal may travel from a transmitter to a receiver over multiple paths, for example, a direct path and one or more reflected paths. In digital cellular phone systems, an equalizer and an error correction decoder are used to process the received signal which may have traveled over multiple paths. In situations where the received signal contains two modulation types, for example, 4-level modulation and 8-level modulation, two equalizers and two error correction decoders are required to process the received signal, where the first equalizer and first error correction decoder are suitable for processing 4-level modulation and the second equalizer and second error correction decoder are suitable for processing 8-level modulation. This increases the hardware cost of a cellular station since multiple equalizers and error correction decoders are required. Furthermore, in a field where products are being manufactured increasingly smaller for convenience, the user of multiple equalizers and error correction decoders require greater printed circuit board (PCB) real estate, resulting in a physically larger product than cellular stations using only one equalizer and error correction decoder.
The present invention is directed to overcoming one or more of the problems discussed above in a novel and simple manner.
SUMMARY OF THE INVENTION
In accordance with the invention, there is disclosed a method and system for the transmission of both 4-level and 8-level signalling symbols using an 8-level modulator. There is further disclosed a method and system for demodulating and error correction decoding a signal containing both 4-level and 8-level modulation.
It is an object of the present invention to provide a method for modulating 4-level signaling symbols using an 8-level modulator, where the method comprises receiving 4-level signaling symbols to be modulated, where each 4-level signaling symbol contains 2-bits of information. The method further includes expanding the 4-level signaling symbols into eight-level signaling symbols, where each 8-level signaling symbol contains 3-bits of information. The method further includes modulating the 8-level signaling symbols.
In a preferred embodiment, the step of expanding the 4-level signaling symbols into 8-level signaling symbols includes manufacturing a third bit for each 4-level signaling symbol and appending the third bit to the 2-bits of information. In this preferred embodiment, the third bit is the exclusive-OR of the 2-bits. In another preferred embodiment, the method includes performing a progressive 45° phase shift between a modulation of consecutive symbols. In a further preferred embodiment, modulating and expanding 4-levels signaling symbols with the 8-level modulator causes the 8-level modulator to produce 4-level modulation. In a yet further embodiment of the invention, the 4-level signaling symbols are a subset of the 8-level signaling symbols. In another preferred embodiment of the invention, the method includes the step of sending an indication signal indicating which of expanded 4-level signaling symbols and 8-level signaling symbols are being transmitted.
It is another object of the present invention to provide a method for demodulation of a received signal containing at least one of 4-level modulation and 8-level modulation where the method includes demodulating the received signal under a first assumption that the received signal contains 4-level modulation and determining a value of a first quality factor by performing error correction decoding on symbols modulated under the first assumption. The method further includes demodulating the received signal under a second assumption that the received signal contains 8-level modulation and determining a value of a second quality factor by performing error correction decoding on symbols modulated under the second assumption. Additionally, the method determines a received modulation present in the received signal using the first and the second quality factors, and demodulates the received signal as the received modulation.
In a preferred embodiment, the step of determining from the first and second quality factors may be performed before the demodulation under the first and the second assumptions is completed. In a further preferred embodiment, the first and second quality factors are determined using metrics generated by an error correction decoder.
It is another object of the invention to provide a method for demodulating a received signal containing at least one of 4-level modulation and 8-level modulation, where the method determines whether 4-level modulation or 8-level modulation is present in the received signal. The method continues by operating a demodulator in a constrained 4-level demodulation mode by restricting possible levels for the received signal to four levels, determining which level out of the four levels is being received, and producing 4-level signaling symbol decisions having 2-bits each if it is determined that 4-level modulation is present. If however, it is determined that 8-level modulation is present in the received signal, the method continues by operating the demodulator in an unconstrained 8-level demodulation mode by determining which level out of 8 possible levels is being received, and producing 8-level signaling symbol decisions having 3-bits each.
In a preferred embodiment, the step of determining whether 4-level modulation or 8-level modulation is present includes the step of receiving an indication signal indicating whether 4-level modulation or 8-level modulation is present in the received signal. In a further preferred embodiment, the indication signal is transmitted using at least one of a SYNCWORD, a CDVCC, and a FACCH message. In a further preferred embodiment, the step of determining whether 4-level modulation or 8-level modulation is present includes the step of using a predetermined transmission format to determine whether a 4-level signaling symbol or an 8-level signaling symbol is present in the received signal.
It is another object of the invention to provide a method for decoding a received signal containing at least one of 4-level signaling symbols and 8-level signaling symbols, the method comprises receiving a signal, demodulating
Dent Paul W.
Ramesh Rajaram
Coats & Bennett P.L.L.C.
Ericsson Inc.
Nguyen Dung X
Vo Don N.
LandOfFree
Method and system for the transmission, reception and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for the transmission, reception and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for the transmission, reception and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3028898