SSB Beam Planner
Plan a 5G NR SSB burst set. Pick a frequency range and SSB subcarrier spacing and the tool derives the burst-set case (A–E), Lmax candidate count, and the exact OFDM-symbol positions inside the 5 ms half-frame per 3GPP TS 38.213 §4.1.
FR1 uses 15/30 kHz. FR2 uses 120/240 kHz.
5 ms half-frame timeline (140 OFDM symbols at SSB SCS)
Each coloured block is a 4-symbol SSB candidate. Hover to highlight its row in the table below.
Candidate SSB start positions (8 beams)
| Beam # | First symbol (l) | Slot | Symbol in slot |
|---|---|---|---|
| #0 | 2 | 0 | 2 |
| #1 | 8 | 0 | 8 |
| #2 | 16 | 1 | 2 |
| #3 | 22 | 1 | 8 |
| #4 | 30 | 2 | 2 |
| #5 | 36 | 2 | 8 |
| #6 | 44 | 3 | 2 |
| #7 | 50 | 3 | 8 |
About SSB burst sets
A 5G NR Synchronization Signal Block (SSB) is 4 OFDM symbols wide (PSS, PBCH, SSS, PBCH) and occupies 240 subcarriers. The gNB transmits up to Lmax of these in a single burst set, each beamformed in a different direction. The UE performs beam-sweep reception during initial access and picks the strongest SSB index. TS 38.213 §4.1 defines five cases (A–E) for how those candidate SSBs are placed in the 5 ms half-frame.
Case A (15 kHz) and Case C (30 kHz) use the symbol set {2, 8} + 14n. Case B (30 kHz, multiplexed with LTE) uses {4, 8, 16, 20} + 28n. Case D (120 kHz) and Case E (240 kHz) are FR2-only and carry up to 64 candidate SSB indices for the much tighter pencil beams needed at mmWave.
Related tools
How to use the SSB Beam Planner
- Choose the frequency range. Select FR1 (sub-3 GHz / 3–6 GHz) or FR2 to bound the maximum beam count Lmax.
- Set the beam count L. Pick how many SSB beams to sweep (4, 8 or up to 64) for your sector plan.
- Set the periodicity. Choose the SSB burst period (e.g. 20 ms) to model how often the sweep repeats.
- Review the sweep timing. See where each SSB index lands in the half-frame and the time cost of one full sweep.
- Map to coverage. Relate the beam count to the angular slice each beam covers across the sector.
Frequently asked questions
- How many SSB beams can a cell use?
- The maximum SSB count Lmax depends on frequency range: up to 4 below 3 GHz, up to 8 from 3–6 GHz, and up to 64 in FR2 (above 6 GHz). Each SSB index marks one beam in the sweep, and the actual number deployed can be fewer than Lmax if the operator does not need full angular coverage.
- Why does FR2 allow 64 SSB beams?
- FR2 uses narrow pencil beams to overcome higher path loss and oxygen absorption at millimetre wave, so each beam covers only a slim angular slice. To paint a whole sector you need many of them, and the SSB sweep cycles through all 64 indices in turn so a UE can find the best beam during initial access.
- How long does a full SSB burst sweep take?
- All SSBs in a burst fall inside a 5 ms half-frame window, and the burst set repeats on the SSB periodicity (5, 10, 20, 40, 80 or 160 ms, default 20 ms for initial access). The individual SSB symbol positions inside the half-frame follow the Case A–E patterns in TS 38.213, which differ by subcarrier spacing.
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