Digital Broadcasting System and Method of Processing Data

1. A method of processing a broadcast signal in a broadcast transmitter, the method comprising: identifying a null data packet included in an input stream that includes the null data packet and a first broadcast data packet for a first service; deleting the identified null data packet in the input stream; randomizing first broadcast data of the first broadcast data packet in the input stream in which the null data packet is deleted; first encoding the randomized first broadcast data systematically; interleaving the first-encoded first broadcast data; and transmitting the broadcast signal including the interleaved first broadcast data, wherein the broadcast signal further includes second broadcast data for a second service multiplexed with the first broadcast data and information for identifying the first broadcast data and the second broadcast data, and wherein the first broadcast data and the second broadcast data have a different robustness level.

2. The method of claim 1 , wherein the first broadcast data are randomized after a sync byte in the first broadcast data packet including the first broadcast data is removed.

3. The method of claim 1 , further comprising: second encoding the interleaved first broadcast data.

4. The method of claim 1 , wherein the null data packet is included in the input stream in order to accommodate variable data rate services in the input stream having a constant bit rate.

5. A broadcast transmitter for processing a broadcast signal, the broadcast transmitter comprising: an input processor for identifying a null data packet included in an input stream that includes the null data packet and a first broadcast data packet for a first service, and deleting the identified null data packet in the input stream; a randomizer for randomizing first broadcast data of the first broadcast data packet in the input stream in which the null data packet is deleted; a first encoder for first encoding the randomized first broadcast data systematically; an interleaver for interleaving the first-encoded first broadcast data; and a transmitting unit for transmitting the broadcast signal including the interleaved first broadcast data, wherein the broadcast signal further includes second broadcast data for a second service multiplexed with the first broadcast data and information for identifying the first broadcast data and the second broadcast data, and wherein the first broadcast data and the second broadcast data have a different robustness level.

6. The broadcast transmitter of claim 5 , wherein the first broadcast data are randomized after a sync byte in the first broadcast data packet including the first broadcast data is removed.

7. The broadcast transmitter of claim 5 , further comprising: a second encoder for second encoding the interleaved first broadcast data.

8. The broadcast transmitter of claim 5 , wherein the null data packet is included in the input stream in order to accommodate variable data rate services in the input stream having a constant bit rate.