Mumbai university > Comp > SEM 8 > Mobile Communication

Marks: 5M

Year: Revised 2012

• Variable rate data is sent on the reverse CDMA channel.

• Code symbol repetition introduces redundancy when the data rate is less than 9600 bps. A data randomizer is used to transmit certain bits while turning the transmitter off at other times.

• When data rate is 9600 bps all interleaver output bits are transmitted. When data rate is 4800 bps, half of the interleaver output bits are transmitter and so forth.

• Data in each 20 ms frame is divided into 16 power control groups, each with 1.25ms. Some are gated-on some are gated-off.

• The data randomizer ensures that every repeated code symbol is transmitted exactly once. During the gated-off process, the mobile station reduces its EIRP either by at least 20 db with respect to the most recent gated-on period or to the transmitter noise floor, whichever is greater. This reduces interference to other mobile stations operating on the same reverse CDMA channel.

• The data burst randomizer generates a masking pattern of 0’s and 1’s that randomly masks the redundant data generated by code repetition process. A block of 14 bits taken from the long code determines the masking pattern.

• The last 14 bits of the long code used for spreading in the second to last power control group of the previous frame are used to determine the random mask for the gating. These 14 bits are denoted as, b0, b1, b2, ........ , b13 where b0 represents earliest bit and b13 represents latest bit.

• For the data rates is 9600 bps transmission occurs on all 16 power control groups.

• For the data rates is 4800 bps transmission occurs on all 8 power control groups given as,

  b0 ,2 + b1 ,4 + b2 ,6 + b3 ,8 + b4 ,10 + b5 ,12 + b6 ,14 + b7.

• For the data rates is 2400 bps transmission occurs on all 4 power control groups given as,

  • b0 if b8 = 0, or 2 + b1, if b8 = 1

  • 4 + b2 if b9 = 0, or 6 + b3, if b9 = 1

  • 8 + b4 if b10 = 0, or 10 + b5, if b10 = 1

  • 12 + b6 if b11 = 0, or 14 + b7, if b11 = 1

• For the data rates is 1200 bps transmission occurs on all 2 power control groups given as,

  • b0 if ( b8 = 1 and b12 = 0), or 2 + b1 if ( b8 = 1 and b12 = 0), or 4 + b2 if ( b9 = 0 and b12 = 1), or 6 + b3 if ( b9 = 1 and b12 = 1)

  • 8 + b4 if (b10 = 0 and b13 = 0), or 10 + b5 if (b10 = 1 and b13 = 0), or 12 + b6 if (b11 = 0 and b13 = 1), or 14 + b7 if (b11 = 1 and b13 = 1).