How does beam scheduling work in 5G NR?

The gNB MAC scheduler operates per-slot (0.5 ms at 30 kHz SCS) and makes three allocation decisions: 1) Beam-to-slot mapping: which Tx beams are active in this slot. Limited by the number of analog beamforming chains (typically 2-8 in FR2). If the gNB has 64 beams but 4 analog chains, only 4 beams can be active simultaneously. 2) UE-to-beam assignment: which UE is served by which beam, based on beam reports (best SSBRI/CRI). UEs with the same best beam are co-scheduled via MU-MIMO if their spatial signatures are sufficiently different. 3) PRB allocation within each beam: standard proportional-fair or round-robin scheduling assigns frequency resources to UEs within each active beam. The beam scheduling order creates a beam sweeping pattern: in TDM mode, the scheduler cycles through beam groups across slots, ensuring all beams are served within a scheduling period (typically 5-20 ms).

What is beam hopping in satellite scheduling?

Beam hopping is a satellite beam scheduling technique where a limited number of active beams hop across a larger set of spot beam positions in a time-multiplexed pattern. A GEO HTS satellite may have 200+ spot beam positions but only 20-40 active beams at any instant (limited by amplifier count and DC power). The beam hopping scheduler allocates dwell time to each beam position proportional to traffic demand: high-demand beams get more time slots, low-demand beams get fewer. The hopping pattern repeats on a superframe cycle (typically 10-100 ms). Advantages over fixed beams: 1) Traffic-adaptive: matches capacity to demand without over-provisioning. 2) Power-efficient: total satellite DC power is shared across fewer simultaneous beams, each with higher EIRP. 3) Spectrum-efficient: full frequency reuse across all beams (color-1 reuse). Defined in DVB-S2X Annex E for standardized beam hopping.

How is inter-beam interference managed in scheduling?

Inter-beam interference occurs when adjacent beams operate on the same frequency simultaneously (spatial-domain multiplexing). Management strategies: 1) Beam grouping: schedule adjacent beams in different time slots (TDM). Group beams by spatial separation, alternating groups across slots. A 4-color reuse pattern ensures no two adjacent beams share time-frequency resources. 2) Power control: reduce transmit power on interfering beams when serving cell-edge UEs. The scheduler coordinates power levels across beams to maintain target SINR. 3) Coordinated scheduling (CoMP): multi-beam joint transmission where interfering beams cooperatively serve cell-edge UEs. Requires beam reports from multiple beams and tight synchronization. 4) Null steering: digitally place nulls in the beam pattern toward co-scheduled UEs in adjacent beams. Requires digital beamforming per-element. The scheduler uses beam-specific CQI/SINR reports to estimate interference and select the scheduling strategy per-slot.

Multi-Beam Systems

Beam Scheduling

/beem SKED-yoo-ling/

The allocation of time, frequency, and spatial resources across multiple beams. In 5G NR, the MAC scheduler maps UEs to beams and assigns PRBs per 0.5 ms slot across 2 to 8 simultaneous analog chains. Dimensions: TDM (beams take turns), FDM (different PRBs), SDM (spatial separation). In HTS satellites, beam hopping allocates dwell time across 200+ spot beams with 20 to 40 active at once (DVB-S2X). Key metrics: aggregate throughput, fairness (Jain's index), utilization, and inter-beam interference.

5G NR: 0.5 ms/slot

Satellite: 10–100 ms cycle

Modes: TDM/FDM/SDM

Understanding Beam Scheduling

Beam scheduling sits at the intersection of physical-layer beamforming and higher-layer resource management. The scheduler must solve a combinatorial optimization problem each slot: given N available beams, K active UEs with beam reports, and limited hardware (analog chains, power amplifiers), select the beam-UE-PRB assignments that maximize system throughput while maintaining fairness.

The challenge intensifies with analog beamforming constraints. A 5G gNB with 64 beams but only 4 analog beamforming chains can serve at most 4 beam directions simultaneously. UEs on different beams must be time-multiplexed, introducing scheduling latency. Digital beamforming relaxes this constraint by enabling all beams simultaneously but at higher power consumption and cost.

Scheduling Capacity Formulas

TDM Beam Capacity:
Per-beam throughput = R_peak × (T_dwell/T_cycle)
64 beams, 4 chains, R=1 Gbps:
Each beam: 1 Gbps × (4/64) = 62.5 Mbps avg

SDM Beam Capacity:
Per-beam: R_peak (all beams simultaneous)
Requires digital BF or hybrid with enough chains
Inter-beam interference reduces effective rate

Satellite Beam Hopping Utilization:
η = ∑(D_i × t_i) / (N_active × T_super)
D_i = demand of beam i, t_i = allocated time
Target η > 85% for cost-effective operation

Scheduling Mode Comparison

Mode	Simultaneous Beams	Interference	Complexity
TDM	1 per chain	None (isolated)	Low
FDM	Multiple (split BW)	Low (freq. sep.)	Medium
SDM	All (spatial sep.)	High (adjacent)	High
Beam hopping	Subset (traffic-based)	None (time-sep.)	Medium

Common Questions

Frequently Asked Questions

5G NR scheduling?

Per-slot (0.5 ms): beam-to-slot mapping (limited by analog chains), UE-to-beam (from beam reports), PRB allocation within beams (proportional-fair). TDM cycles through beam groups every 5 to 20 ms.

Satellite beam hopping?

20 to 40 active beams hop across 200+ positions, dwell time proportional to traffic. Superframe: 10 to 100 ms. Full frequency reuse (color-1). DVB-S2X Annex E standardized. Power-efficient: shared amplifiers.

Inter-beam interference?

Managed via beam grouping (TDM adjacent beams), coordinated power control, CoMP joint transmission, and digital null steering. Scheduler uses per-beam CQI/SINR to select strategy per-slot.

Related Terms

← Beam Report Beam Squint →

Multi-Beam Systems

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