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Numerical: N-TDMA simultaneous users

Short answer

With 25 MHz one-way bandwidth, 20 kHz guard at each edge, and 30 kHz radio channels, channels = (25,000,000 - 40,000)/30,000 = 832. With 3 TDMA users per channel, simultaneous users per cluster = 3 × 832 = 2496.

In the N-TDMA system, it uses one way bandwidth of 25 MHz for the forward (or reverse) channel. The system bandwidth is divided into radio channels of 30 kHz. Guard bands with Bg = 20 kHz are used. Calculate number of simultaneously transmitting users that can be accommodated in each cluster.

N-TDMA (narrowband TDMA, IS-54/IS-136 "US Digital Cellular") divides the band into 30 kHz radio channels, and each radio channel is time-shared by 3 full-rate users (assumed, as in IS-54/136).

Number of radio channels (guard band at both edges of the allocation):

N_ch = (B_t − 2·B_g) / B_c
     = (25 MHz − 2 × 20 kHz) / 30 kHz
     = (25 000 − 40) kHz / 30 kHz
     = 24 960 / 30
     = 832 radio channels

Number of simultaneous users (m = 3 TDMA slots per channel):

N_users = m × N_ch = 3 × 832 = 2496

Here B_t = 25 MHz one-way (forward or reverse) bandwidth, B_g = 20 kHz guard band, B_c = 30 kHz channel bandwidth. Since all these channels can be used inside one cluster (each cell gets a share of them), this is the number of users the cluster can serve at the same time.

Answer: 832 radio channels; with 3 users per channel, 2496 simultaneous users per cluster (if each radio channel carried only one user, it would be 832).

✓ Answer checked by Claude Opus 5.5 (high effort)

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