Voice and data wireless communication system with improved error recovery

Abstract: A method is provided for detecting and recovering from missed control words that signify a transition to or from a speech mode to a data mode in a communication channel. When in a speech mode, speech information is checked for errors. If an error is detected, the next frame or segment of information is assumed to be data information. The data information is examined for valid information such as a valid header. If a valid header is detected, data mode is assumed and if a valid header is not detected, speech mode is assumed.

Description: This invention relates to methods of rectifying a transmission mode. In the past, communication channels were used to communicate both speech and data related information from a transmitter to a receiver. When in a first mode, the communication channel carried speech information and when in a second mode the communication channel carried data information. The transition from speech to data mode or from data to speech mode was indicated through the use of one or more control words. Unfortunately, if the control word was missed or misinterpreted, a receiver would not detect this transition between modes. WO 00 45555 discloses a system and method for low latency multiplexing of real-time and regular data in the same data frame. Real-time data (such as digitized voice) is multiplexed with regular (non-real-time data) across a communications link (such as a modem connection) by inserting the real-time data as a capsule in the same frame with regular data. The real-time data capsule is introduced by an escape sequence. The link's existing packet protocol (such as V.42/HDLC) may be so extended to provide low latency for the real-time data, with minimal impact on existing data-transfer efficiency. Before each data frame is transmitted, the transmitter may determine if real-time data will become available for transmission. If the real-time data will become available before the data frame will have been completely transmitted, the real-time data may be embedded within the frame as a capsule introduced by an escape sequence. The receiver may monitor the data stream for the escape sequence to determine where to start interpreting the data stream as real-time data. After inserting the capsule, the transmitter may resume transmitting the regular data. This continues until the end of the frame is reached. Special escape sequences may be used to prevent regular data sequences equal in value to the primary escape sequences from falsely indicating the beginning of a real-time data capsule. According to this invention there is provided a method as claimed in claim 1. The present invention provides a method for detecting and recovering from missed control words that signify a transition to or from a speech mode to a data mode or from a data mode to a speech mode in a communication channel. When in a speech mode, speech information is checked for errors. If an error is detected, the next frame or segment of information is assumed to be data information. The data information is examined for valid information such as a valid header. If a valid header is detected, data mode is assumed and if a valid header is not detected, speech mode is assumed. Brief Description of the Drawings FIG. 1 illustrates the structure of a communication channel. Detailed Description FIG. 1 illustrates a communication channel in a wireless communication system that can transmit in a speech or data mode to a receiver. The communication channel is broken into segments or frames of a known duration such as 20 milliseconds. When in the speech mode, the frames are broken into an even portion and an odd portion. For example, each 20 millisecond segment or frame 10 is broken into an even and odd portion where the even portion corresponds to the even bits within the frame and the odd portion corresponds to the odd bits within the frame. When transmitting speech information, the speech information is divided diagonally across adjacent frames. For example, a block of speech information is divided between even portion 12 of a preceding frame 10 and odd portion 14 of a subsequent frame 10. As a result, the even bits associated with a block of speech data are in a frame immediately preceding the frame containing the odd bits associated with the same block of speech data. When in the speech mode, control channel information such as information used for handoffs between base stations in a cellular communication system may be used in place of a block of speech data. As with the blocks of speech data, the even bits associated with the control channel block are transmitted in a preceding frame 16 and the odd bits associated with the control channel block are transmitted in the immediately following frame 18. Control channel information is distinguished from speech information through the use of in-band signaling bits. The in-band signaling bits are predetermined bits interleaved with the bits carrying speech or control channel information. The bits are used to indicate when a frame contains speech information, control channel information or other types of information needed to maintain communications. When transitioning from a speech mode to a data mode, a control word such as a data mode control word is included in a frame 20 immediately preceding a frame 22 that will contain data information. The data mode control word is a predetermined pattern that is readily recognized and distinguishable from typical speech data. Once in the data mode, frames 22 through 24 contain data that may be used to convey information such as packet voice control, messaging information such as e-mail information or paging information, Internet information such as, for example, web page information, or other types of information requested by a user. The transition from data mode to speech mode is indicated in a first frame 26 containing speech information by the inclusion of a speech mode control word. The speech mode control word is a pattern of bits that is predetermined and unlikely to be seen in typical speech or data information. Once in the speech mode, speech information is diagonally interleaved using even and odd portions spread across consecutive frames as discussed above. When in the speech mode, speech information is subjected to an error correction process such as a cyclic redundancy check (CRC) by a receiver. If the check indicates there are no errors, speech mode is continued and the receiver continues to treat the information as speech information. If an error is detected, the next frame is assumed to contain data information. The data information is examined for validity by checking for a known bit pattern such as a valid header. If a valid header is detected, data mode is used to receive subsequent frames of information until a speech mode control word indicates otherwise. If the data information fails the examination and does not contain a known bit pattern such as a valid header, speech mode is continued for subsequent frames of information until a data mode is indicated by a data mode control word or by the above-described process.

Claims: A method for detecting and recovering from missed control words that signify a transition between a speech mode and a data mode in a communication channel characterized by the steps of: receiving a communication frame (10); detecting an error in the communication frame (10); checking for valid data information in a subsequent communication frame (10) in response to detecting the error in the communication frame (10); receiving frames (10) as containing data information if valid data information was detected in the subsequent communication frame (10); and receiving frames (10) as containing speech related information (12) if valid data information was not detected in the subsequent communication frame (10). A method as claimed in claim 1, wherein the data information relates to packet voice control information. A method as claimed in claim 1, wherein the data information relates to messaging information. A method as claimed in claim 3, wherein the data information relates to e-mail information. A method as claimed in claim 3, wherein the data information relates to paging information. A method as claimed in claim 3, wherein the data information relates to Internet information. A method as claimed in claim 6, wherein the data information relates to web page information.

Inventors: CONNER KEITH FAULK, CONNER, KEITH FAULK
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 2001
Main classification: H04L12
IPC codes: H04L29, H04L12