Apparatus and method for receiving broadcasting service in a broadcasting system

A broadcasting receiving apparatus and method in a broadcasting system are provided. In a broadcasting receiver, a demodulator demodulates a received broadcasting signal, clips a soft metric value for the demodulated signal to a number of bits, and outputs the clipped soft metric value. A mapper maps the clipped soft metric value to an index value with a resolution inversely proportional to the quantization level of the soft metric value. A deinterleaver deinterleaves the index value and a demapper demaps the deinterleaved index value to a representative value being a soft metric value from a range of soft metric values mapped to the index value. A channel decoder decodes the representative value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(a) of Korean Patent Application No. 2005-65528, filed in the Korean Intellectual Property Office on Jul. 19, 2005, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method for receiving a broadcasting service in a broadcasting system. More particularly, the present invention relates to a broadcasting service receiving apparatus and method for reducing the number of bits of received broadcasting data in a mobile communication system that provides broadcasting service.

2. Description of the Related Art

Mobile communication systems were developed to provide voice service, ensuring mobility for users. With the rapid development of technology and users' demands, mobile communication systems now provide a variety of services. These services include Short Message Service (SMS), e-mail, Internet service, and broadcasting service. The broadcasting service provides digital broadcasting to users by using high data rates which are now available due to drastic technological development. The digital broadcasting takes various forms of services depending on the media. Digital broadcasting services include Digital Multimedia Broadcasting (DMB), Code Division Multiple Access (CDMA)-based BroadCast/MultiCast System (BCMCS), and Multimedia Broadcast Multicast Service (MBMS) based on Universal Mobile Telecommunication System (UMTS).

A description will be made below of a broadcasting service receiving method in a broadcasting receiver illustrated inFIG. 1.FIG. 1is a partial block diagram of a typical broadcasting receiver100.

Referring toFIG. 1, in the broadcasting receiver, a demodulator101demodulates a modulated signal received from a broadcasting station and generates soft metric data for the demodulated signal. A deinterleaver (or buffer)103deinterleaves the soft metric data. A channel decoder105decodes the deinterleaved data in a predetermined method.

In the process, n bits output from the demodulator101are provided to the deinterleaver103without any processing. The size of the deinterleaver103is depth×n. The data depth is defined as a data length stored in the deinterleaver.

Since the broadcasting receiver receives multimedia data compressed by source coding in the broadcasting system, it requires a large-capacity memory buffer. To be more specific, the broadcasting receiver uses a deinterleaver of a mega-bit size for deinterleaving a received signal and a mega-bit×n memory for storing soft metrics. As a result, receiver complexity increases which in turn increases power consumption.

The increasing interest in digital broadcasting is a driving force behind development of many digital broadcasting receivers. To receive better-quality images, algorithms for increasing the performance of a digital broadcasting receiver are under development. Portability is also a requirement for the digital broadcasting receiver because mobility is critical to broadcasting service in a mobile environment. Therefore, decreasing the complexity and power consumption of a digital broadcasting receiver is a challenging issue.

Accordingly, there is a need for an improved apparatus and method for receiving a broadcasting service in a broadcasting system.

SUMMARY OF THE INVENTION

An object of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, exemplary embodiments of the present invention provide a receiving apparatus and method for reducing complexity in a broadcasting system.

Exemplary embodiments of the present invention also provide a receiving apparatus and method for reducing power consumption in a broadcasting system.

According to one exemplary aspect of the present invention, in a broadcasting receiver of a broadcasting system, a demodulator demodulates a received broadcasting signal, clips a soft metric value for the demodulated signal to a number of bits, and outputs the clipped soft metric value. A mapper maps the clipped soft metric value to an index value with a resolution inversely proportional to the quantization level of the soft metric value. A deinterleaver deinterleaves the index value and a demapper demaps the deinterleaved index value to a representative value being a second soft metric value determined from a range of soft metric values mapped to the index value. A channel decoder decodes the representative value.

According to another exemplary aspect of the present invention, in a broadcasting receiving method of a broadcasting system, a received broadcasting signal is demodulated and a soft metric value for the demodulated signal is clipped to a number of bits. The clipped soft metric value is mapped to an index value with a resolution inversely proportional to the quantization level of the soft metric value. The index value is deinterleaved and demapped to a representative value being a second soft metric value determined from a range of soft metric values mapped to the index value. The representative value is decoded.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In order to reduce the complexity of received signal bits, exemplary embodiments of the present invention are implemented by use of a mapper for mapping demodulated data to lower bit values and a demapper for demapping the mapped bit values to the original data in addition to the configuration of a conventional broadcasting receiver.

A broadcasting receiver according to an exemplary embodiment of the present invention will be described with reference toFIG. 2.

FIG. 2is a block diagram of a broadcasting receiver according to an exemplary embodiment of the present invention. Referring toFIG. 2, a broadcasting receiver200includes a demodulator210, a non-linear mapper220, a deinterleaver (or memory)230, a non-linear demapper240, and a decoder250. The other components of the exemplary broadcasting receiver200will not be further addressed herein.

In operation, the demodulator210demodulates a signal received from a transmitter (not shown) and the decoder250decodes input data using a decoding method. The decoder250is a channel decoder for receiving soft metric values as its input, such as a Viterbi decoder. The non-linear mapper220characteristic of the present invention maps an n-bit signal received from the demodulator (or reception buffer)210to an m-bit index. The variable n is the number of bits, within a bit range that does not affect the performance of the decoder250, and m is less than n.

An index value (for example, m) is different from a soft metric value (for example, n) in nature. It reflects the characteristics of an n-bit value. Thus a map table must be made up such that no performance degradation arises from channel decoding.

The non-linear demapper240demaps m-bit information received from the deinterleaver230to an n-bit representative value. The representative value is different from the n-bit soft metric value in nature. One of soft metric values mapped to an index value in the map table, which does not affect performance, is selected as a representative value for the index value for demapping. The representative value is empirically determined, which will be described later in detail. Consequently, the deinterleaver230saves (n−m)×depth of memory space.

FIG. 3is a graph illustrating the PDF of channel decoder input in an exemplary broadcasting receiver. The exemplary channel decoder may be a Viterbi decoder herein. The horizontal axis denotes a quantization level distribution of soft metric values, and the vertical axis denotes occurrence frequency.

Referring toFIG. 3, the occurrence frequency decreases as a soft metric value is farther from the origin a. In other words, as the soft metric value is closer to the origin a, the occurrence frequency increases and thus soft metric values closer to the origin are vulnerable to errors. Reference numeral301denotes n bits which do not affect the performance of the Viterbi decoder. The broadcasting receiver uses only the n-bit range301through clipping. That is, the resolution of a magnitude expressible as a particular bit width within the n-bit range determines an error range. Since the error range decreases as the resolution increases, soft metric values can be expressed more accurately.

Therefore, in order to express an n-bit received signal in decreased m bits without performance degradation in the deinterleaver, a high resolution is given to soft metric values centered around ‘0’ and a low resolution is applied to soft metric values farther from ‘0’. Thus, the afore-mentioned map table must be made up to reflect this characteristic. An example of the map table according to the present invention is given as follows.

In Table 1, actual input soft metric values ranging from −16 to 15 are listed in the leftmost column index values from −4 to 3 are listed in the middle column, and representative values are in the rightmost column. The representative values have the same number of quantization levels as the index values. Thus, n is 5 and m is 3. Referring to the map table, a 5-bit soft metric value is mapped to a 3-bit index value without degrading decoder performance. To be more specific, more quantization levels farther from level ‘0’ are mapped to one index value. For example, five or six quantization levels are mapped to one index value as far as this mapping does not affect system performance, whereas level ‘0’ and level ‘1’ are mapped to one index value. As noted from Table 1, an index value has a wide range of quantization levels as it is farther from level ‘0’.

The index values are mapped to the representative values by the demapper. The representative values offer the same performance as the original soft metric values within their index value ranges during channel decoding. As illustrated in Table 1, the lowest of soft metric values mapped to an index value is selected as a representative value for the index value. While the number of the representative values is equal to that of the index values, the representative values are expressed in the same number of bits as that of the soft metric values.

Now a description will be made of how data is processed in the broadcasting receiver according to exemplary embodiments of the present invention. Two exemplary embodiments of data processing illustrated inFIGS. 4A and 4Bcan be implemented depending on mapping in the map table. The mapping will be described in the context of Table 1, by way of example.

FIG. 4Ais a flowchart illustrating a data processing method according to an exemplary embodiment of the present invention. The map table used in the exemplary embodiment of the present invention has n-bit soft metric values mapped to m-bit index values.

Referring toFIG. 4A, the demodulator210receives a data signal transmitted from an external transmitter in step401and compares the number of bits of a soft metric value for the data signal with n which affects receiver performance in step403. If the bit number of the soft metric exceeds n, the excess bits are clipped in step405. On the other hand, if the bit number of the soft metric value is equal to or less than n, the broadcasting receiver jumps from step403to step407. In step407, the n-bit soft metric value is mapped to an m-bit index value according to the address of the soft metric value in the memory of the mapper. Since the memory has the addresses of all soft metric values, its capacity is so large as to store a 2n×m-bit map table.

Another exemplary embodiment of data processing will be described with reference toFIG. 4B. Steps401to405illustrated inFIG. 4Aare performed in the same manner and thus their description is not provided herein.

Referring toFIG. 4B, a comparator receives data clipped to n bits in step405and converts an address range within which the n-bit signal falls to an m-bit index value address in step421. The mapper reads an index value at the converted address in step423. For example, if an input soft metric value falls within the range of levels 11 to 15, its address is converted so that the soft metric value is mapped to an index value 3.

The mapper and the demapper will be described in more detail with reference toFIGS. 5A,5B and6.

FIG. 5Ais a block diagram of the mapper220according to an exemplary embodiment of the present invention.

Referring toFIG. 5A, the mapper220checks the address of a soft metric value and then maps the soft metric value to an index value corresponding to the address of the soft metric value. If the soft metric value has n bits and the index value is expressed in m bits, a memory221of the mapper220has a 2n×m map table.

FIG. 5Bis a block diagram of the mapper220according to another exemplary embodiment of the present invention.

Referring toFIG. 5B, the mapper220includes a comparator223and a memory225. The comparator223determines a range within which an input soft metric value falls and generates an address according to the range. For example, if the soft metric value is level 6, it falls within a range from level 5 to level 10 and thus the comparator223generates an address for the range. The memory225outputs an index value corresponding to the address in the map table. Compared to the first exemplary embodiment of the mapper220, the memory225has a 2m×m map table because the map table lists m-bit index values and m addresses rather than include all soft metric values.

The demapper240illustrated inFIG. 2will be described with reference toFIG. 6. The configuration and operation of the exemplary demapper240applies commonly to the first and second exemplary embodiments.

Referring toFIG. 6, the demapper240demaps a deinterleaved index value to a representative value. A map table for demapping is stored in a memory241. The memory241is of a 2m×n size.

FIG. 7is a graph illustrating non-linear mapping with different resolution levels according to exemplary embodiments of the present invention. The x axis represents index values to which quantization levels are mapped by the mapper220, and y axis represents the quantization levels of signals input to the mapper220. The level intervals on the x axis represent 4-bit index values according to exemplary embodiments of the non-linear mapping of the present invention.

Referring toFIG. 7, a 6-bit resolution703means that the original 6 bits are mapped 6 bits, in other words no mapping is performed. A 4-bit resolution701means that input 6 bits are mapped to 4 bits. That is, data can be represented more accurately in 6 bits than in 4 bits. In accordance with the non-linear mapping705of the exemplary embodiments of the present invention, a higher resolution709is achieved closer to the origin, while a lower resolution707is given farther from the origin. In other words, quantization levels are mapped with the 6-bit resolution703as they are closer to the origin.

FIG. 8is a graph illustrating the simulated results of the performance of the non-linear mapping according to exemplary embodiments of the present invention. A simulation was performed under the conditions of a multipath fading environment, a velocity of 120 km/h, and a coding rate of 0.5. The x axis represents Signal-to-Noise-Ratio (SNR), and the y axis represents Bit Error Rate (BER).

Relatively left curves provide better performance. A comparison between curve801and curve807tells that the 4-bit non-linear mapping outperforms the 4-bit linear mapping by about 0.4 dB at a BER of 1.00 E-4. Also, the 3-bit non-linear mapping outperforms the 4-bit linear mapping. Consequently, a 4-bit decoder input brings an approximately 0.4 dB gain, with the same effects of a 6-bit decoder input, compared to the conventional technology. Therefore, the memory size can be reduced by ⅓. If the decoder input is 3 bits, the size of the deinterleaver before the decoder can be decreased by about ¼.

As described above, the exemplary non-linear mapping method of the present invention reduces memory complexity in an interleaver or in a receiver with a long memory depth, thereby reducing a chip size and power consumption. Also, since the exemplary non-linear mapper and demapper of the present invention is very low, overall performance can be improved due to the decrease of memory size.