For some consumers, it is desirable to “stay connected” at all times. Current mobile phones support some form of non-voice connectivity such as text messaging, allowing users to subscribe to various information services. These services provide periodic content as it becomes available or on demand from the user. Many mobile phones now support some form of Internet browsing, email access, downloading, and other forms of information transfer.
Standards are currently being established for digital TV broadcasts to a variety of wireless mobile terminals, and the availability of such services is expected to increase in the coming years.
Mobile terminals can take the form of a mobile phone, a personal digital assistant (PDA), a portable media platform (PMP), or any similar product that is capable of storing, processing, playing-back, and communicating digital content wirelessly.
FIG. 1 is a block diagram of a mobile terminal 100P capable of receiving TV signals. Mobile terminal 100P includes a mobile TV receiver 200P and a main processor system 300P. Many mobile terminals include additional functions and interfaces. For example, a mobile phone may include a mobile phone front-end receiver module that allows connectivity to a cellular network such as a GSM, EDGE, or 3G network, a display, a keyboard, headphones, speakers, microphones, a power management system, a camera, an audio/video/image codec and player, and the like.
In the main processor system 300P, the functions are divided into four main operational blocks, including, a cellular subsystem 302, an A/V subsystem 304, a host processor and memory subsystem 306, and a human interface 308. Other interfaces such as WLAN, Bluetooth, GPS, HDMI and the like, not shown in FIG. 1 may also be present.
The mobile TV receiver 200P includes a tuner 202, an analog-to-digital converter (ADC) 204, a demodulator processor and memory 206, and an antenna 208. Radio frequency (RF) communications are received through the antenna 208. The RF signal carries the modulated digital broadcast signal that includes a digital TV signal in addition to other types of broadcast data. The RF signal band, digital modulation scheme, signal bandwidth, and error correction method are specific to the standard utilized by the system. Signal bands between VHF and L band are used, with some systems using higher frequencies. The digital modulation schemes may include QPSK, DQPSK, 16-QAM, 64-QAM and the like. The channel bandwidth to carry TV signals is typically 1.5, 5, 6, 7, or 8 MHz, although other bandwidths are possible. Error correction methods such as convolutional, Reed-Solomon, and Turbo codes may be used to correct multi-byte data packets.
The mobile TV receiver 200P handles RF signal tuning and reception, analog-to-digital conversion, and signal demodulation, and provides digital data to the main processor system 300P for further processing. Cost, size, and power considerations usually demand that a serial interface 110P be used for communication between the receiver and the main processor system. Once the digital data has reached the main processor system 300P, additional processing is performed. Additional processing performed by the main processor system 300P includes error correction, decryption, decoding, play-back and the like.
Like conventional television, mobile TV is a broadcast system, so data flow is primarily from the mobile TV receiver 200P to the main processor system 300P. Control information is sent from the main processor system 300P to the mobile TV receiver 200P to control receiver operation.
One of the standards for mobile TV is DVB-H, or Digital Video Broadcasting-Handheld. DVB-H is an extension of DVB (Digital Video Broadcasting) that addresses the two main issues of broadcasting to a mobile user: power consumption of the terminal and the Doppler Effect—since users may be traveling at relatively high speeds (e.g., in a car or train).
To reduce power consumption, DVB-H utilizes a slicing scheme in which data is sent and received during pre-defined and limited time slots. This allows the receiver to partially shut down outside of the active time slots.
Improved reception quality is achieved by extensive error coding and error correction schemes.
In DVB-H, broadcasts data is sent in the form of fixed size (188 bytes) MPEG-2 (Motion Picture Experts Group) transport stream (TS) packets. FIG. 2 shows the structure of an MPEG-2 TS packet 400P which includes a header 410, a packet identifier (PID) 420, and a payload 430. Depending on the contents of payload 430, packets may be protected packets 432 or non-protected packets 434.
The payload of non-protected packets 434 carries tables of information about the services (Service Information, SI) and programs (Program Specific Information, PSI) that are being broadcast. SI and PSI tables are a part of the broadcast service delivery and are required to navigate through different types of information available in each MPEG-2 TS packet. They are used to decode the selected audio, video, picture, and/or other digital content.
The payload of protected packets 432 carries internet protocol (IP) datagrams, i.e., IP packets. The IP packets contain audio, video, image and graphics data related to each program. Additionally, the IP packets can deliver other types of information such as an electronic service guide (ESG), data files, news, traffic data, financial market data, and graphical newspapers, or any other type of multimedia content. Here and throughout, the phrase “multimedia content” refers to any type of content that may be broadcast to a mobile terminal. Mobile terminals supporting Internet Group Management Protocol (IGMP) additionally may receive content associated with groups to which the mobile terminal has privileges.
FIG. 3 represents a conventional architecture for mobile terminal 100P. The mobile TV receiver 200P is partitioned into a physical layer 210 and a data link layer 220.
In the physical layer 210, the RF tuner may be tuned to a mobile TV channel which is demodulated and converted to a digital signal. The digital signal is initially in the form of DVB symbols 232 which are then converted to MPEG-2 TS packets 234 by DVB-T (Digital Video Broadcasting-Terrestrial) unit 214.
In the data link layer 220, the MPEG-2 TS packets are sorted into protected packets 236 and non-protected packets 238 by MPEG-2 TS unit 222. MPE-FEC (multiprotocol encapsulation-forward error correction) is performed on the protected packets to improve carrier-to-noise ratio (C/N) and Doppler performance in MPE-FEC unit 224. The IP packets 112 are extracted and delivered to the IP processing unit 312 in the main processor system 300P. IP processing unit 312 identifies the IP addresses of the IP packets and filters the packets based on their destination addresses.
Non-protected packets 238 do not receive MPE-FEC decoding and are passed by Non-MPE-FEC unit 226 as TS packets 114 to the SI/PSI processing unit 314 in the main processor system 300P. The SI/PSI tables are extracted from the TS packets by SI/PSI processing unit 314.
The IP processing unit 312 and SI/PSI processing unit 314 residing on the main processor system 300P perform computationally intense tasks. This places a burden on the main processor system.