Currently, a Quadrature Amplitude Modulation (QAM) scheme has been introduced over a Secondary Common Control Physical Channel (SCCPCH) in a Multimedia Broadcast and Multicast Service (MBMS) to improve the throughput of a system.
A Low Chip Rate Time Division Duplex MBMS (LCR TDD MBMS) is introduced below by way of an example. The LCR TDD MBMS with a 16QAM scheme may adopt four timeslot formats as illustrated in FIG. 1, which specify an amount of data transmitted in and constituent fields of respective timeslots as well as whether to carry Transport Format Combination Indicator (TFCI) information in the transmitted data. The TFCI information is used to indicate a combining mode of the data. For example, the TFCI information indicates to a recipient that the first 20 bits in its received data of 80 bits relate to a first set of data and the last 60 bits relate to a second set of data. As illustrated in FIG. 1, no TFCI information is required to be carried in transmitted data in the two timeslot formats with serial numbers of “0” and “2”, and TFCI information of 8 bits is required to be carried in transmitted data in the two timeslot formats with serial numbers of “1” and “3”.
Currently, occupancy of two 5 ms timeslots, i.e., 10 ms, is required for transmission of a data frame in the LCR TDD MBMS with the 16QAM scheme. Referring to FIG. 2, first and second timeslots are occupied for a data frame of 10 ms, and if TFCI information of 8 bits is carried in the data frame, the TFCI information is divided into two halves, and the first and second 4-bit halves of TFCI information are arranged respectively at corresponding locations in the first and second timeslots. Taking the first timeslot as an example below and as illustrated in FIG. 2, data transmitted in the first timeslot is divided into the first and second parts of data between which midamble codes are sandwiched for channel estimation as specified in the timeslot formats as illustrated in FIG. 1, so that the first half of TFCI information is arranged following the first part of data in the first timeslot in order to transmit the TFCI information; and alike the second half of TFCI information is arranged following the first part of data in the second timeslot. As such, the TFCI information of 8 bits can be transmitted to the recipient in the data frame. The data frame is retransmitted at an interval of 10 ms in the case of a Transmission Time Interval (TTI) of 20 ms/40 ms/80 ms.
In the prior art, various information is subject to a loss during transmission thereof, and since the data length of TFCI information is only 8 bits in the LCR TDD MBMS with the 16QAM scheme, the recipient apparently fails to demodulate corresponding part of data according to obtained TFCI information if the TFCI information is subject to a substantial loss during transmission thereof.
An existing solution to the foregoing issue is as follows:
Referring to FIG. 3, TFCI information is firstly mapped to a LCR TDD 16QAM constellation for modulation prior to addition thereof into a data frame in the LCR TDD MBMS in order to maintain the signal strength of the TFCI information. As illustrated in FIG. 3, there are sixteen energy points in the LCR TDD 16QAM constellation, each of the energy points is identified with a binary code with a data length of 4 bits, the intersection of Q and I coordinate axes is referred to as the origin of the LCR TDD 16QAM constellation, and the distance of each energy point from the origin is associated with the power of the energy point so that the energy point further from the origin has larger power. Therefore in a practical application, four energy points closest to the origin each are referred to as a low energy point or a minimum power point, four energy points furthest from the origin each are referred to as a high energy point or the maximum power point, and remaining eight energy points each are referred to as an intermediate energy point or an intermediate power point. For modulation of the TFCI information, the TFCI information of 8 bits is mapped unbiasedly to two of the energy points in the LCR TDD 16QAM constellation to maintain specific signal strength of the TFCI information. For example, the TFCI information of “11011000” is divided into two halves of “1101” and “1000”, and the two halves of TFCI information are mapped respectively to the two energy points identified with “1101” and “1000” for modulating.
Unfortunately, the foregoing method can not be used to satisfactory because although the TFCI information of 8 bits is mapped to the first and second energy points in the LCR TDD 16QAM constellation, the modulated TFCI information may still fail to attain ideal signal strength if the first and/or second energy point is a low energy point closest to the origin, such as “1000”, thus resulting in an influence upon the effect of demodulation at the recipient; and on the other hand, multiple mapping of different TFCI information may occur during modulation, and if there is a considerable difference between the number of times that the TFCI information is mapped to the low energy points and the number of times that it is mapped to the high energy points, a relatively large peak-to-average ratio (the ratio of peak to average) may arise in the system to consequently cause fluctuation of average power in the system and a consequential influence upon stability of the system.