What is spectral efficiency and how does it relate?

Spectral efficiency (SE) measures throughput per unit bandwidth, in bits/s/Hz. It quantifies how efficiently the RF bandwidth is used for data transmission. 5G NR achieves 30 bps/Hz peak SE with 256-QAM and 8x8 MIMO. LTE peaks at ~15 bps/Hz. Wi-Fi 6 achieves ~10 bps/Hz. Shannon's limit bounds SE to log2(1+SNR): at 30 dB SNR, the limit is ~10 bps/Hz per stream. MIMO multiplies this by the number of spatial streams, so 8x8 MIMO at 30 dB SNR approaches ~80 bps/Hz theoretical maximum.

How does RF bandwidth differ from network bandwidth?

RF bandwidth is measured in Hertz and describes the frequency range occupied by a signal or passed by a filter. Network bandwidth is measured in bits per second and describes data-carrying capacity. They are related but not equal: a 100 MHz RF channel (Band n41, 100 MHz BW) can carry 800 Mbps to 2 Gbps of network bandwidth depending on modulation, coding, MIMO, and overhead. The conversion factor is spectral efficiency (bps/Hz). Higher-order modulation and more MIMO layers increase network bandwidth without increasing RF bandwidth.

Communications

Network Bandwidth

Q: How is 5G NR peak throughput calculated?

5G NR peak throughput follows the 3GPP formula: Data Rate = v_layers × Q_m × f × R_max × N_PRB × 12 / T_s × (1 - OH), where v_layers is MIMO layers (up to 16), Q_m is modulation order (8 for 256-QAM), f is scaling factor, R_max = 948/1024, N_PRB is resource blocks (273 for 100 MHz at 30 kHz SCS), 12 is subcarriers per PRB, T_s is symbol duration, and OH is overhead. For single carrier 100 MHz with 4 MIMO layers and 256-QAM: ~1.7 Gbps. With 8 component carriers (800 MHz total) and 16 layers: ~47 Gbps theoretical peak.

/NET-werk BAND-width/

The maximum data throughput capacity of a communication link, measured in bits per second (bps). In RF wireless systems, network bandwidth depends on channel bandwidth (Hz), modulation order (bits/symbol), coding rate, MIMO spatial streams, and protocol overhead. A 5G NR 100 MHz channel delivers 0.8 to 2 Gbps of network bandwidth depending on conditions. Distinguished from RF bandwidth (Hz): the conversion factor is spectral efficiency (bps/Hz).

Units: bps (Mbps, Gbps)

5G Peak SE: ~30 bps/Hz

Shannon Limit: log₂(1+SNR)

Understanding Network Bandwidth

Network bandwidth is what end users experience as "speed." While RF engineers think in Hertz (channel bandwidth), network engineers and consumers think in bits per second (throughput). The bridge between these is spectral efficiency: how many bits per second can be carried per Hertz of RF bandwidth. Higher modulation orders (256-QAM vs. QPSK), more MIMO layers, and better coding push spectral efficiency higher.

Shannon's channel capacity theorem sets the theoretical maximum: C = B × log₂(1 + SNR). In practice, 5G NR achieves about 60 to 70% of Shannon's limit. The gap is due to cyclic prefix overhead, control channels, reference signals, and practical coding constraints. MIMO effectively multiplies capacity by the number of independent spatial streams.

Throughput Calculation

5G NR Throughput Formula:
Rate = v × Q_m × f × R_max × N_PRB × 12 / T_s × (1 − OH)
v = MIMO layers, Q_m = mod order

100 MHz @ 30 kHz SCS, 4×4 MIMO, 256-QAM:
4 × 8 × 0.926 × 273 × 12 × 28000 × 0.86
≅ 1.7 Gbps

Shannon Limit:
C = B × log₂(1 + SNR)
100 MHz @ 20 dB SNR: 100M × 6.66 = 666 Mbps/stream

Technology Spectral Efficiency

Technology	Peak SE (bps/Hz)	MIMO	Modulation
5G NR	~30	Up to 16 layers	256-QAM
LTE-A Pro	~15	Up to 8 layers	256-QAM
Wi-Fi 6E	~10	Up to 8 streams	1024-QAM
DVB-S2X	~5	Single stream	256-APSK

Common Questions

Frequently Asked Questions

How is 5G NR peak throughput calculated?

3GPP formula: Rate = v × Q_m × f × R_max × N_PRB × 12 / T_s × (1-OH). Single 100 MHz carrier, 4 MIMO, 256-QAM: ~1.7 Gbps. 8 carriers (800 MHz), 16 layers: ~47 Gbps theoretical peak.

What is spectral efficiency?

Throughput per unit BW (bps/Hz). 5G NR: 30 bps/Hz peak. LTE: ~15. Wi-Fi 6: ~10. Shannon limit: log₂(1+SNR) per stream. MIMO multiplies by spatial streams. 8x8 at 30 dB SNR: ~80 bps/Hz theoretical max.

RF vs. network bandwidth?

RF BW: Hertz (frequency range). Network BW: bps (data capacity). Conversion: spectral efficiency (bps/Hz). 100 MHz RF at 8 bps/Hz SE = 800 Mbps network BW. Higher modulation and more MIMO increase network BW without more RF BW.

Related Terms

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