What is the difference between bit rate and baud rate?

Baud rate (symbol rate) is the number of symbol transitions per second. Bit rate = baud rate times bits per symbol. For QPSK (2 bits/symbol): a 1 Msymbol/s baud rate yields 2 Mbps. For 256-QAM (8 bits/symbol): 1 Msymbol/s yields 8 Mbps. They are equal only for binary modulation (1 bit/symbol).

What is Shannon capacity?

Shannon's theorem gives the maximum error-free bit rate: C = B * log2(1 + SNR), where B is bandwidth and SNR is linear signal-to-noise ratio. A 20 MHz channel with 20 dB SNR: C = 20e6 * log2(101) = 133 Mbps. No coding scheme can exceed this, but modern LDPC codes approach within 1 dB.

Gross vs net bit rate?

Gross bit rate includes all transmitted bits: payload, FEC redundancy, headers, guard intervals, and pilot symbols. Net bit rate (throughput) is the useful payload data rate. For 5G NR: gross rate includes LDPC parity, DMRS overhead, and CP. Net/gross ratio (spectral efficiency) is typically 0.6-0.85 depending on MCS and overhead configuration.

Signal Processing

Bit Rate

Bit Rate (data rate) is the number of bits transmitted or processed per second, measured in bits per second (bps). It is the fundamental capacity metric for digital communication links. Bit rate equals the symbol rate (baud) multiplied by the number of bits encoded per symbol: R_b = R_s × log₂(M), where M is the modulation order. The maximum achievable bit rate over a channel is bounded by Shannon's capacity: C = B·log₂(1+SNR).

Category: Signal Processing

Unit: bps (bits/second)

Understanding Bit Rate

Bit rate connects modulation, bandwidth, and SNR. Higher-order modulations pack more bits per symbol, increasing bit rate for a given bandwidth. But each step up in modulation order requires approximately 3 dB more SNR to maintain the same BER. Shannon's theorem sets the theoretical maximum: no real system can exceed C = B·log₂(1+SNR) regardless of coding or modulation.

Gross bit rate includes all transmitted bits (payload + FEC + headers + pilots). Net bit rate (throughput) is the useful data delivered to the application. The ratio depends on the coding rate, overhead structure, and protocol efficiency.

Bit Rate Relationships

Bit rate from modulation:
R_b = R_s × log₂(M) × R_code × N_streams

Shannon capacity limit:
C = B × log₂(1 + SNR)

Example: 20 MHz, 64-QAM, R=3/4, 2 streams:
R_b = 20M × 6 × 0.75 × 2 = 180 Mbps (gross)

Bit Rate by Technology

Technology	Bandwidth	Max Modulation	Peak Rate
Wi-Fi 6	160 MHz	1024-QAM	9.6 Gbps
5G NR (FR1)	100 MHz	256-QAM	~4.2 Gbps
5G NR (FR2)	400 MHz	256-QAM	~20 Gbps
LTE-A	20 MHz	256-QAM	~300 Mbps

Common Questions

Frequently Asked Questions

Bit rate vs baud rate?

Baud = symbol transitions/s. Bit rate = baud × bits/symbol. QPSK at 1 Msps = 2 Mbps. 256-QAM at 1 Msps = 8 Mbps. Equal only for binary modulation.

Shannon capacity?

C = B·log₂(1+SNR). 20 MHz channel, 20 dB SNR: C = 133 Mbps. Modern LDPC codes approach within 1 dB of this limit.

Gross vs net?

Gross includes FEC, headers, pilots. Net is payload only. Typical net/gross ratio: 0.6-0.85 depending on MCS and overhead.

Related Terms

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