Backhaul (Telecom)
Understanding Telecom Backhaul
Every cell tower generates user data that must reach the internet. When you stream video on your phone, the data travels from the gNB antenna to the baseband unit at the cell site, then across the backhaul link to a central aggregation point, through the mobile core network, and out to the content server. The backhaul link is the bottleneck: if your cell site can serve 5 Gbps of air interface throughput but only has a 1 Gbps backhaul pipe, users will never see more than 1 Gbps aggregate.
Backhaul Transport Technologies
- Fiber: Virtually unlimited capacity (10-100 Gbps per wavelength). Sub-millisecond latency. Highest deployment cost due to trenching. Used where available, typically in urban areas and along existing utility corridors.
- Microwave (6-42 GHz): Point-to-point licensed links with 100 Mbps to 2 Gbps capacity. Line-of-sight range of 5 to 50 km depending on frequency and dish size. Deployed in days. About 50% of the world's cell sites use microwave backhaul.
- E-band (70-80 GHz): High-capacity mmWave links with 10+ Gbps using 2 GHz channels. Shorter range (1-3 km) due to higher atmospheric attenuation. Lightly licensed in most countries. Ideal for 5G small cell backhaul in urban environments.
- Satellite (LEO/GEO): Used where terrestrial options are impossible (remote islands, maritime, disaster recovery). GEO latency is 250+ ms. LEO constellations (Starlink, OneWeb) reduce this to 20-40 ms with 100-500 Mbps capacity.
Link Budget Calculation
Backhaul is the transport network segment that connects cell site base stations (eNodeBs in LTE, gNBs in 5G NR ) to the mobile core network....
Key specifications:
-42 GHz | -80 GHz | 5 Gbps | 1 Gbps | -100 Gbps
Throughput: R = Nlayers×B×ηSE×(1−OH)
Backhaul Technology Comparison
| Technology | Capacity | Range | Latency | Deploy Time | Cost/Site |
|---|---|---|---|---|---|
| Fiber | 10-100 Gbps | Unlimited | <1 ms | 6-18 months | $50K-$200K |
| Microwave (18 GHz) | 1-2 Gbps | 10-30 km | <1 ms | 1-2 weeks | $15K-$30K |
| E-band (80 GHz) | 10+ Gbps | 1-3 km | <1 ms | 1-2 weeks | $10K-$25K |
| LEO Satellite | 100-500 Mbps | Global | 20-40 ms | Days | $500-$2K/mo |
| GEO Satellite | 50-200 Mbps | Global | 250+ ms | Days | $1K-$5K/mo |
Key Equations
FSPL = 20log(d) + 20log(f) + 32.44 dB
d in km, f in MHz
Link margin:
M = Pt + Gt + Gr − FSPL − Lmisc − RSLthreshold
Rain attenuation:
A = γR × deff dB
Comparison
| Aspect | Backhaul (Telecom) Spec | Typical Range | Impact | Design Note |
|---|---|---|---|---|
| Primary function | Backhaul is the transport network segmen... | Application-dep. | Critical | Verify in sim |
| Operating range | It carries aggregated user traffic from... | Application-dep. | Critical | Verify in sim |
| Performance | Backhaul links use fiber optic, microwav... | Application-dep. | Critical | Verify in sim |
| Integration | Understanding Telecom Backhaul Every cel... | Application-dep. | Critical | Verify in sim |
| Trade-off | The backhaul link is the bottleneck: if... | Application-dep. | Critical | Verify in sim |
Frequently Asked Questions
Why use microwave instead of fiber for backhaul?
Fiber provides the highest capacity but requires trenching that can take 6-18 months and cost $20K-$100K per mile in urban areas. Microwave links deploy in days with just two antenna mounts and a clear line of sight. For rural sites, rooftop small cells, and developing markets where fiber does not exist, microwave at 6-42 GHz delivers 100 Mbps to 2 Gbps at a fraction of the cost. About 50% of global cell sites use microwave backhaul.
What is the difference between backhaul and fronthaul?
Backhaul carries processed user data from the base station to the core network. Fronthaul carries raw radio samples from a Remote Radio Unit (RRU) to a centralized Baseband Unit (BBU), requiring much higher bandwidth (25 Gbps per sector for 5G eCPRI) and lower latency (under 100 microseconds). C-RAN architecture uses fronthaul; traditional distributed RAN uses only backhaul.
What bandwidth does 5G backhaul require?
A 5G macro site with three sectors running 100 MHz of n78 bandwidth can generate 3-5 Gbps aggregate. With carrier aggregation and MIMO, peak throughput exceeds 10 Gbps. Operators deploy E-band (71-86 GHz) links supporting 10 Gbps over 1-3 km using 2 GHz channels and 256-QAM modulation.