This “Product How-To” article focuses how to use a certain product in an embedded system and is written by a company representative.
Digital audio broadcasting (DAB) is a digital radio system originally developed by the Eureka 147. It can deliver a richer experience than traditional FM broadcast because it enables radios to provide more than just better sound quality and more channels – it was also designed to provide rich multimedia content to users, such as electronic program guides, region-specific information such as weather and traffic updates, and realtime multimedia broadcast of news and stock information.
Beyond offering users greater functionality and quality than traditional FM, DAB also allows users to enjoy these services on-the-move without having to put up with noisy, hard-to-hear reception.
The technology is more resilient against mobile condition effects such as fading due to its OFDM-based scheme. Moreover, unlike with traditional FM broadcast, an OFDM scheme enables a single frequency network to cover a large territory.
Consequently, there is increasing demand for DAB receivers to be in portable mobile applications such as in MP3 players, PDAs, portable multimedia players and mobile phones. In these applications, power consumption is a critical issue in determining the viability of such receiver solutions.
By considering the transport frame structure used in the Eureka 147 DAB standard, key system blocks in the RF tuner and in the baseband of the power cycling system may be power cycled. It can be used to reduce the overall power consumption of the system.
|Figure 1: Digital audio broadcast transmission frame structure is built up with OFDM symbols received from either the digitized I/Q interface or the IF interface.|
The DAB transmission frame structure is built up with OFDM symbols received from either the digitized I/Q interface or the IF interface in Figure 1, above.
The first two symbols make up the synchronization channel (SC); the next three symbols make up the fast information channel (FIC), while the remaining 72 (144 for TM III) symbols carry the data of the main service channel (MSC). The symbols in the MSC contain not only audio, but also other service data.
Multiplex configuration info
In the DAB multiplex, several services are grouped together in a single ensemble, and each service may be composed of different service components. The essential component of a service – which is typically audio, but may also be data – is called the primary service component. In addition, the service may be augmented by optional secondary service components.
|Figure 2: DAB service provides for efficient and flexible use of resources by allowing components to be shared.|
The DAB service structure allows for efficient and flexible use of resources by allowing components to be shared among several services (Figure 2 above).
For example, traffic information in the traffic message channel or service information may be two secondary service components. This also allows for services to change the set of components at different program times.
The information pertaining to the configuration of the DAB ensemble is managed by the multiplex configuration information (MCI). The MCI serves the following five principal functions:
1. To define the organization of the subchannels in terms of their position and size in the CIF and their error protection;
2. To list the services available in the ensemble;
3. To establish the links between service and service components;
4. To establish the links between service components and subchannels, and;
5. To signal a multiplex reconfiguration.
From the DAB service structure and the transmission frame structure, the following may be observed:
The phase reference symbols in the SC are essential for synchronizing the transmission frame. Once steady state is reached, however, the receiver can be off during the null symbol.
The symbols in the FIC are essential for providing the channel decoder with the structure and configuration of the multiplex and MSC.
The DAB service structure is such that the service components are contained within discrete subchannels, which are in turn composed of one or more integral capacity units (CUs).
The MCI provides information to the addresses of the CUs required to decode the components of any service.
The DAB ensemble typically contains more than one service.
Hence, when receiving a particular DAB service, DAB decoders can just decode the SC, FIC and symbols of the CIF containing the CUs that make up the subchannels of components of that particular service. Most of the time, it is sufficient for the baseband decoder to be in standby mode, consuming less power.
Future Waves' Fenix FNX-14701LP DAB tuner chip can use the power cycling strategy to significantly reduce its power consumption. During the period when the MSC is transmitting other subchannel information, the DAB decoder doesn't need to decode those OFDM symbols.
Consequently, the FNX14701LP doesn't have to supply the DAB decoder with information at those times. Hence, it can also be operated in standby mode at significantly lower power consumption. These periods of inactivity are signaled to the FNX14701LP via a fast interrupt pin by a compatible baseband signal processor.
The amount of inactivity will depend on the level of error protection and bit rate of the service; it will affect the duration in which the baseband and the RF front-end can be in standby mode. For typical audio reception with an audio data rate of 128Kbps, the RF power consumption may be reduced by as much as 70 percent through power cycling.
Calvin Sim is VP of Product Development at Future Waves Pte Ltd