1. Introduction
2. Simulation assumptions
2.1. Evaluation methodologies
Urban microcell (UMi) | Urban macrocell (UMa) | Rural macrocell (RMa) | |
---|---|---|---|
Layout | Hexagonal grid | Hexagonal grid | Hexagonal grid |
Inter-site distance | 200 m | 500 m | 1732 m |
Channel model | Urban micro model | Urban macro model | Rural macro model |
Carrier frequency | 2.5 GHz | 2 GHz | 800 MHz |
User speed | 3 km/h | 30 km/h | 120 km/h |
2.2. System configuration
Parameter | Description | Value | |
---|---|---|---|
TDD
|
FDD
| ||
BW | Total bandwidth | 20 MHz | 2 × 10 MHz |
N
FFT
| Number of points in full FFT | 2048 | 1024 |
F
s
| Sampling frequency | 22.4 MHz | 11.2 MHz |
Δ
f
| Subcarrier spacing | 10.9375 kHz | |
To = 1/Δ
f
| OFDMA symbol duration without cyclic prefix | 91.43 μs | |
CP | Cyclic prefix length (fraction of T0) | 1/16 | |
T
s
| OFDMA symbol duration with cyclic prefix | 97.143 μs | |
T
f
| Frame length | 5 ms | |
N
F
| Number of OFDMA symbols in frame (excluding switching gaps) | 50 | 51 |
R
DL-UL
| Ratio of DL to UL | Five DL subframes, three UL subframes | Eight DL subframes for DL and UL |
T
duplex
| Duplex time | TTG + RTG = 165.71 μs | N/A |
Topic | Description | IEEE 802.16 m parameter |
---|---|---|
Basic modulation for data | Modulation schemes for data | QPSK, 16QAM, 64QAM |
Basic modulation for control | Modulation schemes for control | QPSK |
Duplexing scheme | TDD or FDD | TDD/FDD |
Subchannelization for data | Contiguous/Distributed Resource Units and permutations | - Subband LRU (SLRU) as defined in Sections 15.3.5.1-15.3.5.3 of [3]; 12 equal-size allocations spanning the complete duration of the time resources (DL portion of the TDD frame, DL FDD frame) NLRU as defined in Sections 15.3.5.1-15.3.5.3 of [3]; 6 equal-size allocations spanning the complete duration of the time resources (DL portion of the TDD frame, DL FDD frame) |
Subchannelization for control | Contiguous/distributed resource units and permutations | DLRU as defined in Sections 15.3.5.1-15.3.5.3 of [3] |
Downlink Pilot Structure | Pilot structure, density etc. | Depends on the number of streams per allocation:1, 2, 3, and 4 pilot streams as defined in Section 15.3.5.4.1 of [3]; 2 dB pilot power boosting for 1, 2 streams and 0 dB power boosting for 3, 4 streams |
Multi-antenna Transmission Format for data | Multi-antenna configuration and transmission scheme | - In the case of SLRU:6-bit transformed codebook; adaptive switching among one stream SU-MIMO, two stream MU-MIMO, three stream MU-MIMO and four stream MU-MIMO In the case of NLRU: long-term BF by using the quantized long-term covariance matrix or wideband PMI; adaptive switching among one stream SU-MIMO, two stream MU-MIMO, three stream MU-MIMO and four stream MU-MIMO |
Multi-antenna transmission format for A-A-MAP | Multi-antenna configuration and transmission scheme | OL SFBC + non-adaptive precoding (T
x
diversity) |
Receiver structure | Receiver interference awareness | MMSE for both channel estimation and data detection |
Data channel coding | Channel coding schemes | Convolutional turbo coding (CTC) 1/3 |
Control channel coding for A-A-MAP | Channel coding schemes and block sizes | As described in Section 15.3.6.3.2.2 of [3] with MLRU size equal to 56 tones |
Scheduling | Demonstrate performance/fairness criteria in accordance to traffic mix | Proportional Fair for full buffer data |
Link adaptation | Modulation and coding schemes (MCS), CQI feedback delay/error | Choice of 16 MCS schemes inclusive of coding rate and rate matching, see Section 15.3.12.1.2 of [3] |
Link to system mapping | MI-based PHY abstraction | MMIB PHY abstraction [2] |
HARQ | HARQ transmission specifics | Chase Combining Asynchronous, adaptive, 3 subframe ACK/NACK delay, maximum 4 HARQ retransmissions, minimum retransmission delay 3 subframes |
Interference model | Co-channel interference model, fading model for interferers, number of major interferers, threshold | Explicitly modeled Average interference on used subcarriers per LRU (subband or miniband) in PHY abstraction |
Control signaling | Message/signaling format, overheads | Signaling errors were modeled for A-A-MAP and HF-A-MAP and sounding estimation errors were modeled for A-MIDAMBLE |
Control channel overhead | L1/L2 Overhead | Dynamic overhead modeling for A-A-MAP and HF-A-MAP and fixed overhead modeling for non-user specific A-MAP (NUS-A-MAP), A-PREAMBLE, A-MIDAMBLE, and SFH |
2.3. Simulation flow
2.4. Control overhead calculation
-
A-A-MAP: The A-A-MAP control overhead is dynamically calculated based on the scheduler allocations in each simulated frame of both DL and UL in each deployment scenario. An A-A-MAP element is transmitted using QPSK 1/2 or QPSK 1/4; all data allocations with SINR higher than 1 dB are assigned a QPSK 1/2 A-A-MAP Information Element (IE). In the case of SLRU, up to three allocations with the same modulation and coding scheme (MCS) for a user are assigned a single A-A-MAP element; this property significantly reduces the control overhead in the case of SLRU permutations. The average DL A-A-MAP and UL A-A-MAP overhead is accounted for in the estimation of the average spectral efficiency and cell-edge user spectral efficiency.
-
HF-A-MAP: The overhead calculation for the HF-A-MAP channel is based on the dynamic calculation of the required ACKs/NACKs from the UL system level simulations for each test environment. Each HF-A-MAP channel is assumed to occupy eight tones in the A-MAP region [13].
-
NUS-A-MAP: 72 subcarriers or 0.75 LRU per subframe is assumed for both TDD and FDD. According to [13], one 5-ms frame is divided into eight subframes each of 0.625 ms duration.
-
A-PREAMBLE: Fixed overhead of one OFDMA symbol per 5 ms frame is assumed for both TDD and FDD.
-
A-MIDAMBLE: Fixed overhead of one OFDMA symbol per 5 ms frame is assumed for both TDD and FDD.
-
SFH: Fixed overhead of 20 LRUs per 20 ms superframe--equal to four 5 ms frames as defined in IEEE 802.16 m [13]--is assumed for both FDD and TDD.
3. Dependence on the evaluation methodology
IMT-Advanced UMi test environment | IEEE 802.16 m test scenario, ITU PB3, 3 degree AS | |||
---|---|---|---|---|
Overhead in LRUs or symbols
|
Overhead in %
|
Overhead in LRUs or symbols
|
Overhead in %
| |
DL A-A-map | 16.6 LRUs | 3.35 | 19.4 LRUs | 3.91 |
DL A-A-map | 8.1 LRUs | 1.63 | 9.5 LRUs | 1.92 |
HF-A-map | 1 LRU | 0.20 | 1 LRU | 0.20 |
NUS-A-map | 3.75 LRUs | 0.76 | 3.75 LRUs | 0.76 |
A-preamble | 1 symbol | 3.23 | 1 symbol | 3.23 |
A-midamble | 1 symbol | 3.23 | 1 symbol | 3.23 |
SFH | 5 LRUs | 1.01 | 5 LRUs | 1.01 |
Total overhead | 13.41% | 14.26% |
IMT-Advanced UMi test environment | IEEE 802.16 m test scenario, ITU PB3, 3 degree AS | |
---|---|---|
Average sector throughput | 44.08 Mbps | 48.25 Mbps |
Average spectral efficiency | 3.55 b/s/Hz/sector | 3.89 b/s/Hz/sector |
Cell-edge user throughput | 999 Kbps | 1392 Kbps |
Cell edge-user spectral efficiency | 0.081 b/s/Hz/user | 0.112 b/s/Hz/user |
4. Dependence on deployment parameters
4.1. Deployment scenarios
UMi test environment | UMa test environment | RMa test environment | |
---|---|---|---|
Average sector throughput | 44.08 Mbps | 33.48 Mbps | 45.63 Mbps |
Average spectral efficiency | 3.55 b/s/Hz/sector | 2.70 b/s/Hz/sector | 3.68 b/s/Hz/sector |
Cell-edge user throughput | 999 Kbps | 818 Kbps | 1091 Kbps |
Cell edge-user spectral efficiency | 0.081 b/s/Hz/user | 0.066 b/s/Hz/user | 0.088 b/s/Hz/user |
-
The carrier frequency of RMa is 800 MHz (see Table 1), which leads to a Doppler frequency of 88.9 Hz. If we compare the Doppler frequency of RMa with that of the UMa test environment, which is 55.6 Hz (30 km/h at 2 GHz carrier frequency), see also Table 1, we can observe that the difference is not significant. As a result, the performance degradation due to channel/sounding estimation and feedback delay errors is not expected to be substantial.
-
If the SINR distributions in Figure 4 are compared, a consistent SINR gain ranging from 0.75 to 1 dB is observed for the RMa test environment for the greater part of the SINR distribution, e.g., from the 5th to the 80th percentile, while the gain is consistent, albeit lower, for the rest of the distribution. The observed SINR gain, which is valid for both cell-edge and cell-center users in the network, can offset the slight performance degradation because of the higher Doppler speed in the RMa test environment compared to UMa.
-
There is higher probability for line-of-sight (LOS) links in the RMa test environment compared to the UMa test environment because of the higher distances expected to be encountered in the RMa test environment, see Table 1 in this article as well as Table Aone-three of Annex 1 in [1]. In addition to the improvement in the geometry, this effect seems to lead to higher BF gains for the RMa test environment as well as more favorable MU-MIMO ZF operation compared to UMa.
ITU PB3 | ITU VA30 | ITU VA120 | |
---|---|---|---|
Average sector throughput | 48.25 Mbps | 37.82 Mbps | 38.69 Mbps |
Average spectral efficiency | 3.89 b/s/Hz/sector | 3.05 b/s/Hz/sector | 3.12 b/s/Hz/sector |
Cell-edge user throughput | 1392 Kbps | 880 Kbps | 918 Kbps |
Cell edge-user spectral efficiency | 0.112 b/s/Hz/user | 0.071 b/s/Hz/user | 0.074 b/s/Hz/user |
ITU PB3 | ITU VA30 | ITU VA120 | |
---|---|---|---|
Average sector throughput | 45.11 Mbps | 34.30 Mbps | 35.30 Mbps |
Average spectral efficiency | 3.64 b/s/Hz/sector | 2.77 b/s/Hz/sector | 2.85 b/s/Hz/sector |
Cell-edge user throughput | 1,310 Kbps | 790 Kbps | 818 Kbps |
Cell edge-user spectral efficiency | 0.106 b/s/Hz/user | 0.064 b/s/Hz/user | 0.066 b/s/Hz/user |
4.2. Antenna configuration
ITU PB3 | ITU VA30 | ITU VA120 | |
---|---|---|---|
Average sector throughput | 31.74 Mbps | 22.82 Mbps | 23.44 Mbps |
Average spectral efficiency | 2.56 b/s/Hz/sector | 1.84 b/s/Hz/sector | 1.89 b/s/Hz/sector |
Cell-edge user throughput | 905 Kbps | 595 Kbps | 645 Kbps |
Cell edge-user spectral efficiency | 0.073 b/s/Hz/user | 0.048 b/s/Hz/user | 0.052 b/s/Hz/user |
UMi test environment | UMa test environment | RMa test environment | |
---|---|---|---|
Average sector throughput | 42.90 Mbps | 28.40 Mbps | 40.18 Mbps |
Average spectral efficiency | 3.46 b/s/Hz/sector | 2.29 b/s/Hz/sector | 3.24 b/s/Hz/sector |
Cell-edge user throughput | 904 Kbps | 655 Kbps | 890 Kbps |
Cell edge-user spectral efficiency | 0.073 b/s/Hz/user | 0.053 b/s/Hz/user | 0.072 b/s/Hz/user |
5. Dependence on system parameters
5.1. Duplex mode (TDD/FDD)
UMi test environment | UMa test environment | RMa test environment | |
---|---|---|---|
Average sector throughput | 35.29 Mbps | 27.10 Mbps | 36.80 Mbps |
Average spectral efficiency | 3.53 b/s/Hz/sector | 2.71 b/s/Hz/sector | 3.68 b/s/Hz/sector |
Cell-edge user throughput | 838 Kbps | 641 Kbps | 880 Kbps |
Cell edge-user spectral efficiency | 0.084 b/s/Hz/user | 0.064 b/s/Hz/user | 0.088 b/s/Hz/user |
5.2. Permutations
UMi | UMa | RMa | ||||
---|---|---|---|---|---|---|
SLRU (from Table 6)
|
NLRU
|
NLRU (from Table 6)
|
SLRU
|
NLRU (from Table 6)
|
SLRU
| |
Average sector throughput | 44.08 Mbps | 41.91 Mbps | 33.48 Mbps | 31.25 Mbps | 45.63 Mbps | 44.02 Mbps |
Average spectral efficiency | 3.55 b/s/Hz/sector | 3.38 b/s/Hz/sector | 2.70 b/s/Hz/sector | 2.52 b/s/Hz/sector | 3.68 b/s/Hz/sector | 3.55 b/s/Hz/sector |
Cell-edge user throughput | 999 Kbps | 818 Kbps | 818 Kbps | 806 Kbps | 1,091 Kbps | 1,029 Kbps |
Cell edge-user spectral efficiency | 0.081 b/s/Hz/user | 0.066 b/s/Hz/user | 0.066 b/s/Hz/user | 0.065 b/s/Hz/user | 0.088 b/s/Hz/user | 0.083 b/s/Hz/user |
5.3. CQI/PMI feedback quantity
Best-3 | Best-4 | Best-6 | Best-9 | UMi results from Table 6 | |
---|---|---|---|---|---|
Average sector throughput | 33.75 Mbps | 34.65 Mbps | 38.45 Mbps | 41.77 Mbps | 44.08 Mbps |
Average spectral efficiency | 2.72 b/s/Hz/sector | 2.79 b/s/Hz/sector | 3.10 b/s/Hz/sector | 3.37 b/s/Hz/sector | 3.55 b/s/Hz/sector |
Cell-edge user throughput | 905 Kbps | 954 Kbps | 954 Kbps | 970 Kbps | 999 Kbps |
Cell edge-user spectral efficiency | 0.073 b/s/Hz/user | 0.077 b/s/Hz/user | 0.077 b/s/Hz/user | 0.078 b/s/Hz/user | 0.081 b/s/Hz/user |
5.4. Sounding, channel estimation, and control signaling errors
UMi | ITU PB3 | |||
---|---|---|---|---|
Without errors
|
With errors (from Table 6)
|
Without errors
|
With errors (from Table 7)
| |
Average sector throughput | 47.99 Mbps | 44.08 Mbps | 47.72 Mbps | 45.11 Mbps |
Average spectral efficiency | 3.87 b/s/Hz/sector | 3.55 b/s/Hz/sector | 3.85 b/s/Hz/sector | 3.64 b/s/Hz/sector |
Cell-edge user throughput | 1,230 Kbps | 999 Kbps | 1505 Kbps | 1,310 Kbps |
Cell edge-user spectral efficiency | 0.099 b/s/Hz/user | 0.081 b/s/Hz/user | 0.121 b/s/Hz/user | 0.106 b/s/Hz/user |
6. The promise of MU-MIMO for technology evolution
IEEE 802.16e 2 × 2 SU-MIMO | IEEE 802.16e 4 × 2 SU-MIMO | IEEE 802.16 m 2 × 2 MU-MIMO | IEEE 802.16 m 4 × 2 MU-MIMO | |
---|---|---|---|---|
Average sector throughput | 8.00 Mbps | 9.27 Mbps | 14.14 Mbps | 22.11 Mbps |
Average spectral efficiency | 1.30 b/s/Hz/sector | 1.51 b/s/Hz/sector | 2.28 b/s/Hz/sector | 3.57 b/s/Hz/sector |
Cell-edge user throughput | 275 Kbps | 375 Kbps | 422 Kbps | 626 Kbps |
Cell edge-user spectral efficiency | 0.045 b/s/Hz/user | 0.061 b/s/Hz/user | 0.068 b/s/Hz/user | 0.101 b/s/Hz/user |