##  [Near-Far Problem](/near-far-problem-0) 

 Definition

A multiple‑access impairment in which a transmitter close to a receiver (or base station) produces a much larger received power than more distant transmitters on the same shared resource, so that the stronger signal overwhelms the weaker ones and prevents their correct detection or decoding.

 

 

 

 

 

 





## Principle

Principle

Received power imbalance on a shared channel reduces the SINR of distant users; without power control, scheduling, orthogonalization, or interference cancellation, the strongest signals dominate reception and can suppress weaker users’ access.

 

 

 

 

 





## Demonstration

Demonstration

Illustrative scenario → In an uplink to a base station using a shared code or random access, Mobile A is 10 m from the base station while Mobile B is 500 m away. A’s signal arrives with much higher power, causing the base station receiver to decode A while B’s packet is lost due to insufficient SINR despite correct transmission parameters.

 

 

 

 

## Misapplication

Misapplication

Equating the near‑far problem with purely physical proximity or with hidden terminals. The semantic error is ignoring pathloss, fading and power control: ‘near’ refers to received power dominance, not geographic distance alone.

 

 

 

 

 





## Consequence

Consequence

Unfair access, decreased aggregate throughput for distant users, higher retransmission and latency for weak users; practical responses include closed‑loop power control, user scheduling, spread‑spectrum power balancing, or successive interference cancellation.

 

 

 

 

## Reversal

Reversal

Systems with orthogonal resource allocation (FDMA/TDMA), effective power control that equalizes received powers, or receivers implementing SIC can largely eliminate the near‑far effect; conversely, in uncontrolled random access or poorly tuned power control, the problem persists.

 

 

 

 

 





## Boundary

Boundary

Clearly within: CDMA uplink or unscheduled shared uplink where no effective power control is applied and one transmitter’s received power dominates. Boundary case: partial power control that reduces but does not equalize received powers. Clearly outside: fully orthogonalized links or centrally scheduled per‑user power allocation producing comparable received powers.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Fairness ↔ Efficiency — aggressive scheduling or power control that enforces fairness can reduce instantaneous throughput or increase control overhead; allowing power disparities can maximize throughput for close users at the expense of distant ones.

 

 

 

 

 





## Synthesis

Synthesis

The near‑far problem is fundamentally about received‑power asymmetry on a shared medium; solving it requires controlling or exploiting power relationships (control, scheduling, orthogonality or advanced receivers) rather than solely altering physical node placement.