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Downloading and Using Files

User File Data Downloads

Chapter 4 173

Because timeslots are configured and enabled within the signal generator, a user file can be

individually assigned to one or more timeslots. A timeslot cannot have more than one data

source (PN sequence or user file) specified for it. The amount of user file data that can be

mapped into hardware memory depends on both the amount of PRAM available on the

baseband generator, and the number and size of each frame. The amount of PRAM required

for a framed transmission is calculated as follows:

PRAM required =

size of normal GSM timeslot

timeslots per frame

speech multiframe(TCH)

superframe

size of normal GSM timeslot = 156.25 bits

timeslots per frame = eight timeslots.

speech multiframe(TCH) = 26 frames

superframe = 51 speech mulitframes

For example, to calculate the number of bytes to generate a superframe for GSM:

= 156.25

= 1,657,5000 bytes.

Multiple User Files Selected as Data Sources for Different Timeslots

If two or more user files are selected for a framed transmission, the amount of PRAM required

is determined by the user file that generates the largest number of frames. In order to

generate continuously repeating data patterns, each user file must be long enough to

completely fill an integer number of timeslots. In addition, all user files must meet the

“multiple of 8 bits” and “enough PRAM memory” requirements to be correctly modulated.

For example, user file #1 contains 114 bits and fills the data fields of a normal GSM timeslot,

and user file #2 contains 148 bits for a custom GSM timeslot. In order to correctly transmit

these data patterns as continuously repeating user files without discontinuities, both data

patterns must be repeated four times. Therefore, user file #1 contains 456 bits, and user file 2

contains 592 bits. Each user file will then create exactly four frames in pattern RAM.

When two or more user files generate different numbers of complete frames, the user files will

repeat on different cycles. All user files will restart when the user file that generates the

largest number of frames repeats. For example, user file #1 needs four frames to completely

transmit its data, and user file #2 needs only three. User file #2 will repeat after the third

frame, and again when user file #1 repeats. See Figure 4-3. If these were integer multiples of

each other, both user files would be continuous, and user file #2 would repeat after two

frames.