Pulse or digital communications – Testing – Signal noise
Reexamination Certificate
1999-09-13
2002-07-30
Pham, Chi (Department: 2631)
Pulse or digital communications
Testing
Signal noise
C375S222000, C375S225000
Reexamination Certificate
active
06426971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to communication systems. Specifically, the present invention relates to systems for predicting the signal to interference and noise ratio (SINR) of a received signal to facilitate data rate control in wireless communication systems.
2. Description of the Related Art
Wireless communication systems are used in a variety of demanding applications including search and rescue and business applications. In addition, wireless communication systems are increasingly employed to transfer computer data in office network and Internet applications. Such applications require efficient and reliable communication systems that can effectively operate in electrically fading and noisy environments and that can handle high data transfer rates.
Cellular telecommunication systems are characterized by a plurality of mobile stations (e.g. cellular telephones or wireless phones) in communication with one or more base stations. The communications link from a base station to a mobile station is the forward link. The communications link from the mobile station to the base station is the reverse link.
Signals transmitted by a mobile station are received by a base station and often relayed to a mobile switching center (MSC). The MSC in turn routes the signal to a public switched telephone network (PSTN) or to another mobile station. Similarly, signals are often transmitted from the public switched telephone network to a mobile station via a base station and a mobile switching center. Each base station governs a cell, a region within which a mobile station may communicate via the base station.
In typical mobile communication systems, information is encoded, modulated, and transmitted over a channel and received, demodulated and decoded by a receiver. In many modern communication systems, such as Code Division Multiple Access (CDMA) cellular networks, the information is encoded digitally for channel noise, capacity, and data security reasons. A convolutional encoder or turbo encoder often performs the encoding of the information.
As is well known in the art, a convolutional encoder converts a sequence of input data bits to a codeword based on a convolution of the input sequence with itself or with another signal. Code rate and generating polynomials are used to define a convolutional code. Convolutional encoding of data combined with a Viterbi decoder is a well-known technique for providing error correction coding and decoding of data. Turbo encoders employ turbo codes, which are serial or parallel concatenations of two or more constituent codes such as convolutional codes.
Mobile communication systems are typified by the movement of a receiver relative to a transmitter or vice versa. The communications link between transmitters and receivers in a mobile communication system is a fading channel. Mobile satellite communications systems, having a transmitter on a spacecraft and a receiver on a ground based vehicle, cellular telephone systems and terrestrial microwave systems are examples of fading communication systems. A fading channel is a channel that is severely degraded. The degradation results from numerous effects including multipath fading, severe attenuation due to the receipt via multiple paths of reflections of the transmitted signal off objects and structures in the atmosphere and on the surface, and from interference caused by other users of the communications system. Other effects contributing to the impairment of the faded channel include Doppler shift due to the movement of the receiver relative to the transmitter and additive noise.
Typically, an information signal is first converted into a form suitable for efficient transmission over the channel. Conversion or modulation of the information signal involves varying a parameter of a carrier wave on the basis of the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the channel bandwidth. At a user location, the original message signal is replicated from a version of the modulated carrier received subsequent to propagation over the channel. Such replication is generally achieved by using an inverse of the modulation process employed by the source transmitter.
In a CDMA system, all frequency resources are allocated simultaneously to all users of the cellular network. Each user employs a noise-like wide band signal occupying the entire frequency allocation. The encoder facilitates the encoding of necessary redundant data within each transmission frame to take advantage of the entire frequency allocation, and also facilitates the variable rate transmission on a frame by frame basis.
For voice communication, the capacity of a CDMA system is maximized by having each user transmit only as much data as is necessary. This is because each user's transmission contributes incrementally to the interference in a CDMA communication system. A very effective means of reducing each user's burden on capacity without reducing the quality of service to that user is by means of variable rate transmission. The use of a variable rate communication channel reduces mutual interference by eliminating unnecessary transmissions when there is no useful speech to be transmitted.
Due to the characteristics of voice communication, power control is typically utilized in a CDMA system to guarantee each user a reliable link for certain fixed data rates. Vocoders can provide variable rate source coding of speech data, using the technique described in U.S. Pat. No. 5,414,796, May 9, 1995, entitled “Variable Rate Vocoder”. Once a vocoder generates a sequence of information bits at certain rate, power control will try to adjust the user to transmit as little power as possible that can reliably support the rate. Power control, thus by suppressing each user's contribution to the total interference, facilitates the maximum capacity of a CDMA voice system in the sense that the number of active users is maximized.
For data communication, the parameters, which measure the quality and effectiveness of a system, are the transmission delay required for transferring a data packet and the average throughput rate of the system. Transmission delay is an important metric for measuring the quality of the data communication system. The average throughput rate is a measurement of the efficiency of the data transmission capacity of the communication system. In order to optimize the above parameters for a data communication system, rate control, instead of power control, is typically utilized. The above differences between the voice and data communication systems can be better understood by the following different characteristics between the voice and data communications.
A significant difference between voice services and data services is the fact that the former imposes stringent and fixed delay requirements. Typically, the overall one-way delay of speech frames must be less than 100 msec. In contrast, the data delay can become a variable parameter used to optimize the efficiency of the data communication system. Specifically, more efficient error correcting coding techniques that require significantly larger delays than those that can be tolerated by voice services can be utilized. An exemplary efficient coding scheme for data is disclosed in U.S. patent application Ser. No. 5,933,462, entitled “SOFT DECISION OUTPUT DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS”, filed Nov. 6, 1996, assigned to the assignee of the present invention and incorporated by reference herein.
Another significant difference between voice services and data services is that the former requires a fixed and common grade of service (GOS) for all users. Typically, for digital systems providing voice services, this translates into a fixed and equal transmission rate for all users and a maximum tolerable value for the error rates of the speech frames. In contrast, for data services, the GOS can be different from user to user and can be a parameter optimized to increase the overall
Black Peter J.
Sindhushayna Nagabhushana T.
Wu Qiang
Baker Kent D.
Pham Chi
Phu Phuong
QUALCOMM Incorporated
Wadsworth Philip
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