In 4G LTE, the Uplink Resource Grid is the time-frequency grid over which uplink physical channels and signals are mapped. LTE uplink uses SC-FDMA (Single-Carrier FDMA), which provides lower peak-to-average power ratio than OFDMA. This simulator visualizes 10 subframes (140 symbols, 1 radio frame) for 15 Resource Blocks (180 subcarriers), simplified from 20 MHz bandwidth for visibility.

Resource Grid Structure (3GPP TS 36.211 §5.2)

A Resource Element (RE) is the smallest unit: 1 subcarrier × 1 symbol. A Resource Block (RB) consists of 12 subcarriers and 1 slot (7 symbols for normal cyclic prefix). A Subframe consists of 2 slots (14 symbols total). A Radio Frame is 10 ms and contains 10 subframes (140 symbols).

Display: 10 Subframes = 140 Symbols (1 Radio Frame) | 1 Subframe = 2 Slots = 14 Symbols | 15 RB = 180 Subcarriers

PUSCH — Physical Uplink Shared Channel (TS 36.211 §5.3)

PUSCH carries user data and uplink control information (UCI). It occupies the bulk of the resource grid, excluding regions reserved for PUCCH, DMRS, and PRACH.

PUCCH — Physical Uplink Control Channel (TS 36.211 §5.4)

PUCCH carries uplink control information (HARQ ACK/NACK, CQI, SR). This simulator shows a single UE: in slot 0 it uses the top-most RB (RB 5); in slot 1, with slot hopping enabled, it hops to the bottom-most RB (RB 0) for frequency diversity. Without hopping, it stays at the top RB.

DMRS — Demodulation Reference Signal (TS 36.211 §5.5.1)

DMRS is used for channel estimation and coherent demodulation. PUSCH DMRS uses 1 symbol per slot (index 3). PUCCH DMRS placement depends on format: Format 1/1a/1b (SR, ACK) uses 3 symbols per slot (2, 3, 4); Format 2/2a/2b (CQI) and Format 3 (Carrier Aggregation) use 2 symbols per slot (1, 5). The simulator distinguishes PUSCH DMRS (solid gold) from PUCCH DMRS (striped).

PRACH — Physical Random Access Channel (TS 36.211 §5.7)

PRACH is used for initial access and timing alignment. Per TS 36.211 §5.7, PRACH occupies 6 RB (1.08 MHz) in frequency but uses 1.25 kHz subcarrier spacing (1/12th of 15 kHz), giving 839 active subcarriers plus 13 (top) and 12 (bottom) guard subcarriers. The preamble is a Zadoff-Chu sequence. The time structure comprises: CP (Cyclic Prefix, teal); Preamble Sequence (purple); and Guard Time (GT, dark) for round-trip delay. Preamble Format 0/1/2/3 sets duration and GT: Format 0 (~14.5 km); Format 1 (~77 km); Format 2 (~30 km); Format 3 (~100 km).

SRS — Sounding Reference Signal (TS 36.211 §5.5.3)

SRS is used for uplink channel quality estimation and supports frequency-selective scheduling. It occupies the last symbol (l=13) of configured subframes and uses a comb structure (every 2nd subcarrier) for multiplexing. SRS is not transmitted in PUCCH RBs. srs-SubframeConfig (0–15) determines periodicity and offset per TS 36.211 Table 5.5.3.3-1. UE-specific bandwidth (B_SRS) and start RB define the SRS frequency window.

RRC Parameters for PUCCH (TS 36.331)

PUCCH allocation is configured via RRC signaling. Key parameters from PUCCH-ConfigCommon and PUCCH-ConfigDedicated:

• nRB-CQI: INTEGER (0..98). Number of RBs for CQI reporting (Format 2/2a/2b). Reserved at band edges.
• nCS-AN: INTEGER (0..7). Cyclic shifts for HARQ-ACK in mixed-format RBs. Higher values allow more UEs to share PUCCH.
• n1PUCCH-AN: INTEGER (0..2047). PUCCH resource index for Format 1/1a/1b HARQ-ACK. Determines which RB and cyclic shift the UE uses.
• n2PUCCH: INTEGER (0..119). PUCCH resource index for Format 2/2a/2b/3 (CQI). m = ⌊n2PUCCH / N_sc^RB⌋; same hopping formula applies.
• deltaPUCCH-Shift: ENUMERATED {ds1, ds2, ds3}. Affects resource block calculation for Format 1.

 

Usage

1. Resource Grid / Spectrum tabs: The Resource Grid tab shows the time-frequency grid. The Spectrum tab shows the Power Spectral Density (Welch method) of the SC-FDMA signal. Use Scope to select Radio Frame (full 10 subframes), Subframe, or Symbol; when Subframe or Symbol is selected, use the slider to pick which one.
2. Show PRACH: Toggle visibility of the Physical Random Access Channel (6 RB). The grid shows CP (teal), Preamble (purple, 839 subcarriers @ 1.25 kHz), and GT (dark) as distinct bands. Preamble Format 0/1/2/3 sets duration and GT ratios per TS 36.211. prach-ConfigIndex selects starting subframe. prach-FrequencyOffset sets the starting RB.
3. PUCCH Format: Format 1/1a/1b (SR, HARQ-ACK) uses 3 DMRS symbols per slot (2, 3, 4); Format 2/2a/2b (CQI) and Format 3 (Carrier Aggregation, up to 48 bits) use 2 DMRS symbols per slot (1, 5).
4. RRC Parameters: nRB-CQI (0..98) sets RBs for CQI (Format 2/3). nCS-AN (0..7) is cyclic shifts per RB. n1PUCCH-AN (0..2047) selects which RB the UE uses for Format 1. n2PUCCH (0..119) selects which RB the UE uses for Format 2/3 (CQI). deltaPUCCH-Shift {ds1, ds2, ds3} affects Format 1 resource calculation.
5. Slot Hopping: When enabled, the single UE's PUCCH in slot 1 hops from the top RB to the bottom RB for frequency diversity. When disabled, it stays at the top RB in both slots.
6. Magnification: Zoom the grid from 1× to 5× for easier inspection of individual Resource Elements.
7. Channel checkboxes: Toggle visibility of PUSCH, PUCCH, PUSCH DMRS, PUCCH DMRS, Reserved, PRACH, and SRS. Unchecked channels appear dimmed.
8. SRS Control Panel: srs-SubframeConfig (0–15) selects the 3GPP cell-specific subframe pattern (TS 36.211 Table 5.5.3.3-1). Transmission Comb (k_TC) selects even (0) or odd (1) subcarriers. Start RB (n_RRC) anchors SRS; Bandwidth B_SRS extends upward. Hopping shifts the start RB across subframes for full-bandwidth sounding. SRS appears in the last symbol (l=13), excluding PUCCH RBs.
9. Hover: Move the mouse over any cell to see its subcarrier index (k), symbol index (l), Resource Block number, and channel type in the status bar.
10. Reserved (PUCCH): Hatched regions show RBs where PUSCH cannot be scheduled; only PUCCH or empty resources are allowed there.

Implementation Notes: 3GPP Compliance (TS 36.211 §5.4)

This visualizer implements Mapping Type A (Normal CP) and intra-subframe frequency hopping. The physical RB index n_PRB follows TS 36.211 §5.4.3:

n_PRB = ⌊m/2⌋ if (m + n_s mod 2) mod 2 = 0; else N_RB^UL − 1 − ⌊m/2⌋

where m is derived from n1PUCCH-AN (Format 1) or n2PUCCH (Format 2/3: m = ⌊n2PUCCH / N_sc^RB⌋); n_s is the slot index (0 or 1). Simplifications: The "Mixed RB" (Format 1 + Format 2 in same RB) is not visualized for clarity. Format 3 uses the same RB mapping as Format 2; multiplexing via Orthogonal Cover Codes is not shown.

DMRS & Time-Domain Spreading: Format 1 uses 3 DMRS symbols (2, 3, 4) to support OCC of length 3 for multiplexing multiple UEs on the same frequency. Format 2/3 use 2 DMRS symbols (1, 5).

Scheduling Constraint (PUSCH vs PUCCH Orthogonality)

PUSCH and PUCCH are orthogonal in frequency: the eNodeB scheduler never allocates PUSCH into RBs reserved for PUCCH. The "Reserved (PUCCH)" regions (hatched) show RBs where PUSCH is not allowed. The No-Go zone is the union of CQI (Format 2/3) and ACK/NACK (Format 1) reservations: m_max = max(m_CQI, m_AN) where m_CQI = 2·nRB-CQI − 1. RBs with n_PRB ≤ ⌊m_max/2⌋ (bottom) or n_PRB ≥ N_RB^UL − 1 − ⌊m_max/2⌋ (top) are reserved. Increasing nRB-CQI or n1PUCCH-AN narrows the "PUSCH pipe" in the middle, reducing peak data rate.

Key 3GPP References

• TS 36.211 §5.2 — Uplink physical resource grid.
• TS 36.211 §5.3 — PUSCH mapping.
• TS 36.211 §5.4 — PUCCH and slot hopping.
• TS 36.211 §5.5.1 — Uplink DMRS.
• TS 36.211 §5.5.3 — SRS sequence generation and mapping.
• TS 36.211 §5.7 — PRACH formats.
• TS 36.331 — RRC protocol; PUCCH-ConfigCommon, PUCCH-ConfigDedicated.