Patent Application
20050278601
This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for increasing a reliability of receiving control messages, such as multiframe control messages.
In 2G (generation) and 3G CDMA wireless communication systems, once a mobile unit is assigned to a traffic channel, the control signaling associated with the call is sent over that traffic channel. A majority of control signals can fit into a single over-the-air (OTA) traffic frame. A few critical control messages, e.g., call setup messages, require multiple OTA traffic frames due principally to size.
In prior-art systems, whenever any of the frames of a message fails transmission, the entire message is discarded and must be resent thus using precious airtime. This can be particularly troublesome when the message is a multiframe sequence. Unfortunately, the requirement for perfectly receiving all frames of each multiframe message sequence before the message is usable results in degraded transmission reliability, especially for the multiframe messages, since multiple retransmissions of the multiframe sequence can be required.
Thus, what is needed is a method and apparatus for improving/increasing the reliability of receiving control messages.
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.
In overview, the present disclosure concerns communications systems that utilize receivers to provide service for communications units or more specifically a user thereof operating therein. More particularly, various inventive concepts and principles embodied as a method and apparatus for improving or increasing reliability of receiving single or multiframe control messages for use in equipment with such communications systems will be discussed and disclosed. The communications systems of particular interest are those being deployed and developed such as CDMA (Code Division Multiple Access), W-CDMA (Wideband-CDMA), CDMA2000, 2G (Generation), 2.5G, 3G, UMTS (Universal Mobile Telecommunications Services), GPRS (GSM packet radio service) systems and evolutions thereof that utilize spread spectrum signals, although the concepts and principles have application in other systems and devices.
Examples of control messages or signaling where the principles and concepts of the present invention may be advantageously utilized include, for example, origination, page response, RLP/RLC (radio Link protocol/radio Link control) retransmissions & ACK/NAKs, data burst messages (including short data burst and short message service). The principles and concepts can be utilized on a variety of channel types, including, for example, dedicated (such as the fundamental channel in CDMA systems) channels, common channels (such as the paging and access channels), and other channel types.
The instant disclosure is provided to further explain in an enabling fashion the best modes of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. 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.
It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
Much of the inventive functionality and many of the inventive principles are best implemented with or in one or more conventional digital signal processors (DSPs), or with integrated circuits (ICs) such as custom or Application Specific ICs (ASICs) and corresponding software instructions. 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 programming such DSPs, or generating such ICs with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention, further discussion of such DSPs and ICs, if any, will be limited to the essentials with respect to the principles and concepts employed by the preferred embodiments.
Referring to
We now will disclose and discuss in greater detail the reasons for the decreased reliability of messages, such as multiframe messages and our solutions therefor. In CDMA, once a mobile is assigned to a traffic channel, the control signaling associated with the call is sent over this traffic channel. Many signaling messages in CDMA can fit within one 20 ms Over The Air (OTA) traffic frame. However, there are critical messages that have to be sent over multiple OTA frames due to size. Such messages are often sent during call setup. In one embodiment, the composite frame error rate (FER) for the traffic channel is targeted at 1%. Probability theory shows that the reception of a correct multiframe message is worse than that of a signaling message that can fit within a single over the air transmission.
The probability that an entire multiframe sequence is received successfully during a single attempt is approximately, assuming independent erasures, (1-FER){circumflex over ( )}N where N is the number of successive OTA frames required for the message. For a 1% FER environment the probability that a 3-frame message is successfully received during one attempt is 0.99{circumflex over ( )}3=0.97 which results in an effective message erasure rate of 3%. The probability gets worse the longer the signaling message is. Additionally, there may be times during a call where the RF may temporarily degrade and have a short term FER of 5%, 10% or more. This further decreases the probability of a successful transmission. The prior-art systems try to combat this by simple retransmissions. It should be noted that increasing the reliability of any single frame will improve or increase the reliability of the multiframe sequence or message as well and thus avoid wasting airtime or channel capacity for retransmissions.
A specific problem in, for example, various known CDMA systems is the reception of a status response message. Other systems often have similar messages that can be multiframe or otherwise critical to operation. Failure to receive this message at the infrastructure results in the infrastructure being unable to set up the call, due to receiving insufficient mobile status information. The problem has become worse for 3G mobiles vs. 2G mobiles. The status response message contains a listing of all the service configurations the mobile supports. For a 2G mobile, this results in a message that traverses 3 frames. The newer 3G mobiles are generating a message that traverses 8 frames. When even one of the multiple frames fails reception, the entire message is discarded and the entire multiframe sequence has to be resent—often several times. Each retransmission undesirably extends the call setup time and also increases the likelihood of a failed call setup.
In one embodiment in accordance with the present invention the central base station controller (CBSC) monitors when a multiframe signaling message is imminent. The CBSC is represented by the controller 100, which has been simplified to avoid obscuring the present invention. It will be appreciated that in a practical system the CBSC will have additional elements. When the multiframe signaling message is expected within a predetermined time after being requested by the controller 100, the controller 100 activates the multiframe buffer 112. If the received signaling message fails its CRC16 check, the controller 100 will buffer up the pieces of the multiframe message based on the success of the over the air CRC result. Upon a failure of reception of one or more of the message segments (preferably indicated by an erasure of each unsuccessfully received message segment), the controller 100 preferably will request a retransmission. The controller 100 is aware that the retransmission is imminent and will perform a mix and match operation with previously successfully received pieces or frames of the anticipated signaling message until a combination results in a complete copy of the signaling message. Additional retransmissions are required when the original transmission and the first retransmission do not contain enough successfully received pieces to reconstruct the signaling message. During call set up in particular, the mobile operates in a speak only when spoken to mode. The multiple frame signaling message is the direct result of a query from the controller 100. The controller 100 thus is aware that the mobile unit will be responding only with the requested (multiframe) signaling message. It will be appreciated that, alternatively, in response to discovering the erasure, the controller 100 can send to the mobile unit a negative acknowledgement or no response, instead of requesting the retransmission.
Thus, it should be clear from the preceding disclosure that the present invention provides a method and apparatus for substantially improving the reliability of receiving multiframe control messages. The method and apparatus advantageously does not require any changes in the mobile units, however if needed the same principles and concepts can be applied in a mobile device on a downlink or outbound, base to mobile, channel.
This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
