1. Field of the Invention
The invention relates to radio communications, and, more particularly, to techniques of detecting a particular burst in a communication system.
In the General Packet Radio Service (GPRS)/Enhanced GPRS (EGPRS) system, uplink/downlink carrier is divided into radio frames and each frame is divided into eight time slots. A physical channel is a specified time slot in consecutive frames. There are five bursts that may be transmitted, which are normal burst, frequency correction burst, synchronization burst, dummy, and access burst. A base station (BS) transmits a dummy burst as filler in unused uplink/downlink carrier timeslots. Because the structure of a dummy burst is similar to a normal burst, detecting a dummy burst (or normal burst) may be important in GPRS/EGPRS systems.
For example, USF (uplink Status Flag) information in a normal burst transmitted by a base satiation may notify users able to transmit data on the uplink path in a specific time slot of the next frame. If a user misinterprets a dummy burst as a normal burst, an invalid USF is generated adversely affecting the data transmission rate and potentially dropping the connection. Thus, the ability to distinguish between a dummy burst and a normal burst is desirable.
In one aspect of the invention, a dummy burst detection method is provided. The method begins with generating a dummy burst nominal power ηDB2 of a received burst, wherein the dummy burst nominal power ηDB2 is generated based on the hypotheses that the received burst is a dummy burst. A normal burst nominal power ηNB2 is then generated. The normal burst nominal power ηNB2 is formed based on the hypotheses that the received burst is a normal burst. A likelihood of the received burst is determined according to the dummy burst nominal power ηDB2 and the normal burst nominal power ηNB2.
In another aspect of the invention, a system for detecting a dummy burst is provided. The system comprises a dummy burst nominal power unit, a normal burst nominal power unit, a likelihood unit, and a decision unit. The dummy burst nominal power unit generates a dummy burst nominal power of a received burst, wherein the dummy burst nominal power is formed according to a first hypothesis that the received burst is a dummy burst. The normal burst nominal power unit generates a normal burst nominal power of the received burst, wherein the normal burst nominal power is formed according to a second hypothesis that the received burst is a normal burst. The likelihood unit determines a likelihood of the received burst according to the dummy burst nominal power, the normal burst nominal power, and the noise power of the received burst.
The invention will become more fully understood from the detailed description, given herein below, and the accompanying drawings. The drawings and description are provided for purposes of illustration only, and, thus, are not intended to be limiting of the invention.
In EGPRS (Enhanced GPRS) systems, a data block consists of 4 normal bursts or 4 dummy bursts. 4 normal bursts of one data block have the same modulation scheme, and 4 dummy bursts of one data block use same training sequence. Thus, to prevent channel noise from disturbing the cost function E, the burst cost function E is summed and averaged in step 104. An example of averaged E is shown as following:
where i is the burst index, σi2 is the noise power of the i-th burst. σi2 may be calculated by:
σi2=E[r2]−max[ηDB2,ηNB2], (2)
where E[r2] is the expectation of square of the received burst.
In one embodiment of the invention, such as an EGPRS system in which Gaussian Minimum Shift Keying (GMSK) and 8-ary Phase Shift Keying (i.e., 8-PSK or EPSK) are used, the normal burst nominal power ηNB2 is generated by selecting the larger of ηGMSK2 and ηEPSK2. The GMSK nominal power ηGMSK2 is formed according to a hypothesis that the received burst is a normal burst modulated by Gaussian Minimum Shift Keying (GMSK), and the EPSK normal burst nominal power ηEPSK2 is formed according to hypotheses that the received burst is a normal burst modulated by 8-ary Phase Shift Keying (EPSK). By selecting the larger of radio frequency channel C0 nominal power ηC02 and Cordless Telephony System (CTS) Control Channel (CTSC) nominal power ηCTSC2, the dummy burst nominal power ηDB2 is generated. Similarly, the C0 nominal power ηC02 is formed according to a hypothesis that the received burst is a dummy burst with a C0 sequence, and the CTSC nominal power ηCTSC2 is formed according to a hypothesis that the received burst is a dummy burst with a mapped sequence CTSC. It should be understood that the detection method of the invention is not limited to the described embodiments. Any alternative method for detecting the likelihood of each burst from a dummy burst nominal power and a normal burst is within the scope of the present invention.
The decision unit 208 determines the received burst is a dummy burst if the likelihood of the received burst L exceeds a threshold, where
ηDB2 is the dummy burst nominal energy of the received burst, ηNB2 is the normal burst nominal energy of a received burst, and σ2 is the noise power of the received burst.
In other embodiments, system 20 further comprises a diversity unit 210. The diversity unit 210 collects all the likelihoods of received bursts among a data block, and the decision unit determines a received data block is a dummy burst block if the diversity unit output Ls exceeds a threshold, where
ηDB2(i) is the dummy burst nominal energy of a i-th burst of the received data block, ηNB2(i) is the normal burst nominal energy of the i-th burst of the received data block, and σi2 is the noise power of the i-th burst of the received data block. In EGPRS systems, a data block consists of 4 normal burst or 4 dummy burst. The diversity unit 210 collects the likelihoods of 4 received burst among a data block to generate Ls.
The implementation of dummy burst nominal power unit 202 may vary, depends on which communication system is applied. For example, in the EGPRS system, the dummy burst nominal power unit 202 generates a C0 nominal power and a CTSC nominal burst and selects the larger of C0 nominal power and the CTSC nominal burst nominal power as the dummy burst nominal power. The C0 nominal power is formed according to a third hypotheses that the received burst is a dummy burst with a C0 sequence, and the CTSC nominal burst nominal power is formed according to a fourth hypotheses that the received burst is a dummy burst with a mapped sequence CTSC. Similarly, the implementation of the normal burst nominal power unit 204 may also vary as communication systems. In the EGPRS system, the normal burst nominal power unit 204 generates a GMSK nominal power and an EPSK nominal burst and selects the larger of GMSK nominal power and the EPSK nominal burst nominal power as the normal burst nominal power. The GMSK nominal power is formed according to a fifth hypothesis that the received burst is modulated by GMSK, and the EPSK nominal burst nominal power is formed according to a sixth hypothesis that the received burst is modulated by EPSK.
The dummy burst detection is applicable to various applications, such as Uplink Status Flag detection, Header false alarm, BFI, and others.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
This application claims the benefit of U.S. provisional application Ser. No. 60/825,961 filed Sep. 18, 2006, the subject matter of which is incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
5481561 | Fang | Jan 1996 | A |
6298095 | Kronestedt et al. | Oct 2001 | B1 |
6647000 | Persson et al. | Nov 2003 | B1 |
20020069038 | Cooper | Jun 2002 | A1 |
20020072334 | Dunne et al. | Jun 2002 | A1 |
20040132457 | Sanders et al. | Jul 2004 | A1 |
20060007994 | Lai et al. | Jan 2006 | A1 |
20060121911 | Zhang et al. | Jun 2006 | A1 |
20060198371 | Huang et al. | Sep 2006 | A1 |
20060270442 | Miller et al. | Nov 2006 | A1 |
20070047587 | Kuo et al. | Mar 2007 | A1 |
20070183522 | Garrett et al. | Aug 2007 | A1 |
20080137179 | Li et al. | Jun 2008 | A1 |
20080207141 | O'Keefe et al. | Aug 2008 | A1 |
20090296629 | Lincoln et al. | Dec 2009 | A1 |
Number | Date | Country | |
---|---|---|---|
60825961 | Sep 2006 | US |