Patent Application
20060280159
The present invention relates generally to the field of communications and more particularly to a method and apparatus for optimizing voice communications within a communication system using automatic retransmissions.
Communication systems, such as the commonly known code division multiple access (CDMA) 2000 which is the next generation of the commonly known system based on Interim Standard-95 (IS-95) CDMA standard, or wide-band CDMA (W-CDMA) which is the next generation of the commonly known system based on the global system for mobile communication (GSM) standards, and other such mobile communications systems suffer from a degradation of capacity due to the fading nature of the radio frequency (RF) link. As a mobile device moves in a fading environment, the signal strength vanes and channel capacity is decreased. Improvements to the overall capacity of a communication system can be obtained by improved fading mitigation schemes. Further, voice capacity improvements are essential to the growth of such systems.
There are typically two limiting factors to voice capacity in a CDMA system, one is the RF capacity and the other one is the Walsh code space. (Also known as “Walsh-Hadamard code,” Walsh code is an algorithm that generates statistically unique sets of numbers for use in encryption and cellular communications.) To a certain degree, a tradeoff can be made between these two depending on a system load. For example, there are two radio configurations, RC3 and RC4, for the forward link of a CDMA2000 system. A voice call in RC4 consumes half of the Walsh code space than in RC3, but requires a signal-to-noise ratio (SNR) of approximately 1.15 dB higher than in RC3 for the same frame erasure ratio (FER) under certain channel conditions. With the development of a Selectable Mode Vocoder (SMV), RF efficiency can be further balanced with voice quality or voice activity. SMV contains a set of modes with different mixes of full rate, half rate, quarter rate, and eighth rate frames. The voice quality and RF load generated by a SMV mode depend on the percentages of each type of frame.
The higher the percentage of full rate frames is, the better the voice quality is, but the higher the generated RF load is. There is a half-rate maximum mode, where the highest rate a voice frame can have is half-rate. This was originally designed for scenarios when a network gets congested. It has been found that its quality is satisfactory for push-to-talk applications.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
This invention includes a new transmission method and apparatus for voice vocoder frames by introducing hybrid automatic retransmission requests (H-ARQ) for voice communication services. This invention further provides a new transmission method and apparatus for Enhanced Variable Rate Codec (EVRC) frames, SMV frames, and other voice vocoders' frames, which takes advantage of the RF benefits of H-ARQ.
Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a method and apparatus for voice communication. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of a method and apparatus for voice communication described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method to perform voice communication. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
Communication system 100 includes multiple Base Transceiver Stations (BTS) such as 110,115,120, and at least one mobile units (MUs) 105. Each of the BTS 110, 115, 120 communicate with the at least one mobile unit 105 by transmitting one or more vocoded frames 130, 140, 150 using a plurality of transmission intervals, wherein each of the plurality of transmission intervals is split into a first interval portion and a second interval portion, and further wherein a plurality of code symbols associated with each vocoded frame are divided into a group A and a group B.
The mobile unit 105, for example, can be a mobile cellular telephone, a mobile radio data terminal, a mobile cellular telephone having an attached or integrated data terminal, a two-way messaging device, or an equivalent. Similarly, the mobile unit 105 can be any other electronic device such as a personal digital assistant or a laptop computer having wireless communication capabilities.
The Base Transceiver Stations 110,115,120, and the at least one mobile units 105 communicate using at least one traffic channel 125, 135, 145. For example, the base transceiver stations 110, 115, 120 use the traffic channel 125, 135, 145 for communicating the group A code symbols and the group B code symbols to the mobile unit 105. In one embodiment, the traffic channel includes at least one sub-channel for communicating from the mobile unit 105 to the base transceiver stations 110, 115, 120. The sub-channel, for example, can comprise a control information sub-channel of the traffic channel. The sub-channel can be used to send such signals as acknowledgement signals when communications are successful received by the mobile unit 105 and alternatively negative acknowledgement signals when communications are not successfully received by the mobile unit 105. In one embodiment, the one or more of the traffic channels 125, 135, 145 includes at least one sub-channel for communicating from the base transceiver stations 110, 115, 120 to the mobile unit 105. The sub-channel, for example, can comprise a control information sub-channel of the traffic channel 125, 135, 145. The sub-channel can be used to carry one or more retransmission flags in soft handoff scenarios.
Although not shown, communication system 100 additionally include well known network elements such as Mobile Switching Centers (MSCs), Centralized Base Station Controllers (CBSCs) in a circuit switch network, or such as Radio Network Controller (RNCs), Gatekeepers (GKs) and GateWays (GWs) in a packet switch network. It is contemplated that network elements within the communication system 100 are configured in well known manners with processors, memories, instruction sets, and the like, which function in any suitable manner to perform the function set forth herein.
The base station 200 includes a transmitter 205 for communicating with one or more communication devices such as the mobile unit 105 of the communication system 100. The base station 200 further includes a processor 210 coupled to the transmitter 205 for processing voice communications such one or more vocoded frames. The processor 210, in accordance with the present invention, is adapted to cause the transmitter 205 to transmit a group A code symbols of a vocoded frame using a first interval portion of an interval i to one or more devices such as the mobile unit 105 of
The receiver 305, for example, receives the group A code symbols of the vocoded frame from the base station 200 in
ACK/NAK information can be carried by the control sub-channel. For a mobile unit in soft/softer handoff, special care needs to be taken for ACK/NAK and retransmission. For the reverse link transmission (ACK/NAK from base station), the mobile unit does retransmission only if a NAK is received from all soft/softer legs. For forward link transmission (ACK/NAK from mobile station), the retransmission on individual soft/softer legs is performed if a NAK is received by that leg. Due to the detection reliability, especially when there is significant unbalance among soft/softer legs, not all soft/softer legs can receive NAK signaling correctly. That is, retransmission may happen only on a subset of soft/softer legs because some of the soft/softer legs do not detect the NAK sent by mobile unit correctly. Since the mobile unit has no knowledge of whether a base station receives the NAK or not, it hence does not know if a retransmission happens on a soft/softer leg. This causes a problem within the mobile unit when it tries to do combining on signals from soft/softer legs: on one hand it loses RF efficiency if it doesn't combine a leg when there is retransmission; on the other hand it hurts receiver performance by taking in noise if it combines a leg when there is no retransmission. It also prevents the mobile unit's receiver to correctly scale the soft code symbols from the retransmission for channel decoding. In accordance with the present invention, the concept is to transmit a flag on the control sub-channel to indicate if a retransmission for frame i−1 is present at the second half of transmission interval i.
Referring to
As shown, the operation begins with Step 500 in which a parameter N is set to 1 and an interval I is set to i. Next, in Step 505, a group A code symbols of a Nth vocoded frame is transmitted from a transmitter to a receiver using a first interval portion of an interval I. For example, the transmitter can transmit the group A code symbols to the receiver using a traffic channel of the communication system.
Next, the operation continues to Step 520 in which the receiver decodes the group A code symbols received at the first interval portion of the interval I. Next, in Step 525, the receiver performs a cyclic redundancy code check on the first interval portion of the interval I. Next, in Step 530, the receiver determines whether or not the first interval portion of the interval I passed or failed the cyclic redundancy code check. When the first interval portion of the interval I passed the cyclic redundancy code check, the operation can optionally proceed with Step 535 in which the receiver generates and sends an acknowledgment (ACK) signal to the transmitter. The operation then ends.
When the first interval portion of the interval I fails the cyclic redundancy code check in Step 530, the operation continues with Step 540 in which the receiver generates and sends a negative acknowledgment (NAK) signal to the transmitter. For example, the receiver can send the negative acknowledgment (NAK) signal to the transmitter using a sub-channel of the traffic channel of the communication system. The sub-channel, for example, can be a control information sub-channel of the traffic channel.
Next, in Step 545, the transmitter transmits to the receiver group B code symbols of the Nth vocoded frame using a second interval portion of an interval I+1. It will be appreciated that the interval can alternatively be any I+m, where m is a positive integer. It will be further appreciated that the transmitter can transmit the group B code symbols to the receiver using a traffic channel of the communication system. The operation then continues to node B.
Next, in Step 550, receiver combines code symbols from the first interval portion of interval I, with the code symbols from the second interval portion of interval I+1. For example, the combining can comprise performing a hybrid automatic retransmission request (H-ARQ) with incremental redundancy (IR) on the group A code symbols in the first interval portion of interval I with the group B codes symbols in the second interval portion of the interval I+1. Next, in Step 555, the receiver decodes the combined code symbols from the first interval portion of interval I, with the code symbols from the second interval portion of interval I+1. Next, in Step 560, the receiver performs cyclic redundancy check on the decoding results from both the code symbols of the first interval portion of interval I and the code symbols from the second interval portion of interval I+1. Next, in Step 565, the receiver determines whether or not the cyclic redundancy code check succeeds. When the cyclic redundancy code check passes, the operation continues to node B of
Referring to
Referring to
Next, and when retransmission identification combining was not active in Step 705, the operation continues to Step 720 in which it is determined whether or not signal strength combining is activated. When signal strength combining is active, the operation continues to Step 725 in which the signal strength of each of the received transmissions is measured; and those with signal strength values greater than a predetermined signal strength are identified. Next, in Step 730, the receiver combines group A and group B code symbols of the vocoded frame using the received transmissions with signal strength values greater than a predetermined value.
Next, and when the signal strength combining is not active in Step 720, the operation continues to Step 735 to determine if any other combining method is active. When another combining method is activated, the operation continues to Step 740 and that combining is accomplished. Next, and when no other combining method is active, the operation ends.
The present invention, as described herein, provides a novel transmission method and apparatus for voice vocoder frames by introducing H-ARQ for voice service thereby improving radio frequency efficiency. The H-ARQ operation is introduced for voice service with the same high Walsh code efficiency as existing systems. Maximal ratio combining is enabled for soft/softer handoff without complexity of blind detection of retransmission on individual soft/softer leg. The present invention thus provides a novel method and apparatus to increase voice capacity in voice communication systems.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
