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5G Flexible Transceiver for Physical Layer Evaluation

Basic overview The aim of this proposal is to extend the flexible PHY software component made available by the eWINE project with MIMO technologies. The goal is to utilize the second independent RF chain of the USRP SDR to employ Alamouti space-time coding (STC) combined with GFDM. This technique, firstly introduced for OFDM based wireless […]

September 26, 2018/by najeebgafar@gmail.com

5G physical layer specifications

The 5G specifications have been published as the 3GPP 38 series. Here we look at the physical layer specifications. 38.211: Physical channels and modulation The scope is to establish the characteristics of the Layer-1 physical channels, generation of physical layer signals and modulation, and to specify: Definition of the uplink and doecewnlink physical channels Frame structure […]

September 26, 2018/by najeebgafar@gmail.com

5G Flexible Transceiver for Physical Layer Evaluation

September 26, 2018/by najeebgafar@gmail.com

5G physical layer specifications

September 26, 2018/by najeebgafar@gmail.com

Full Sized Blog Element (Big Preview Pic)

5G Flexible Transceiver for Physical Layer Evaluation

Basic overview

The aim of this proposal is to extend the flexible PHY software component made available by the eWINE project with MIMO technologies. The goal is to utilize the second independent RF chain of the USRP SDR to employ Alamouti space-time coding (STC) combined with GFDM. This technique, firstly introduced for OFDM based wireless transmission systems, increases the reliability of the data transfer by transmitting multiply copies of the data stream. However, it has not yet been applied on the GFDM flexible waveform generation framework and, since GFDM is a nonorthogonal waveform, its combination with STC is not a straight forward approach.

GFDM Library – How to use

In this library, only basic functions for GFDM transmission, signal generation, and naive reception are included, nothing fancy like channel estimation/equalization, iterative receivers, etc. The functions are grouped into several parts:

get_* These functions return objects that are commonly used for GFDM simulations.
calc_* These functions calculate (not only) performance values based on the passed objects.
do_* These more complex functions do actual simulation steps.

Remark: To use the library functions, you must include the library folder and subfolders to the MATLAB path.

The GFDM library has a folder with examples of use for the functions (GFDM_libraryexamples). With the purpose of illustration, an example file (GFDM_libraryexamplesser_in_awgn.m) for generation of a GFDM SER (Symbol Error Rate) curve is detailed below.

For the GFDM configuration, a parameter structure p contains the configuration of the GFDM system.

% GFDM configuration
p = get_defaultGFDM('BER');
p.pulse = 'rc_fd';
p.a = 0.5;

GFDM Transmitter

Create random data symbols

% create symbols
s = get_random_symbols(p);

The function get_random_symbols(p) returns a sequence of integers in range 0 ⋯ 2????−1 which are the transmitted data symbols.

QAM-Modulate the symbols to QAM symbols and map the symbol stream to the data matrix

% map them to qam and to the D matrix
D = do_map(p, do_qammodulate(s, p.mu));

Map the integers in range 0 ⋯ 2????−1 to a quadratic QAM modulation using the MATLAB function qammod. The one-dimensional symbol stream is mapped to the data matrix D according to the values of ???????????????? and ????????????????. Empty sub-carriers and sub-symbols in D are set to zero. Afterwards there is the possibility to insert specific pilots or other information in the slots where no data is present.

GFDM-Modulate the data matrix

x = do_modulate(p, D);

The matrix ???? is processed with the GFDM modulation scheme to produce a time domain signal with length ???????? that can be processed further. The transmitted signal is applied to an AWGN channel using the function do_channel. A channel object from MATLAB can be used as input parameter for this function for different channels.

% channel -> AWGN
xch = do_channel(x, 1, snr(si));% channel -> AWGN
xch = do_channel(x, 1, snr(si));

Source: luciano@inatel.br

September 26, 2018/by najeebgafar@gmail.com

5G physical layer specifications

The 5G specifications have been published as the 3GPP 38 series. Here we look at the physical layer specifications.

38.211: Physical channels and modulation

The scope is to establish the characteristics of the Layer-1 physical channels, generation of physical layer signals and modulation, and to specify:

Definition of the uplink and doecewnlink physical channels
Frame structure and physical resources
Modulation mapping (BPSK, QPSK, etc.)
OFDM signal generation
Scrambling, modulation and up-conversion
Layer mapping and precoding
Physical shared channel in uplink and downlink
Reference signal in uplink and downlink
Physical random-access channel
Primary and secondary synchronization signals

5G transmission numerologies

5G supports OFDM numerologies (μ) that can scale across the sub 6GHz to the mm-waves. The subcarrier scales from 15 KHz to 240 KHz (Δf).

Supported transmission numerologies in 5G (Credit: 3GPP TS 38.211 V15.1.0 Table 4.2–1)

The OFDM symbol duration and the cyclic prefix duration scale based on the numerology.

Scalable OFDM configuration (Credit: Ericsson)

The selection of numerology will depend upon the size of the cell and the frequency band. Large cells have a large time dispersion at the receiver. A large cyclic prefix needed to counter the larger time dispersion. Higher numerologies are preferable for higher frequencies as the wider subcarrier is less susceptible to phase noise.

Selecting the numerology based on cell size and frequency (cred: Ericsson)

Frames and subframes

Downlink and uplink transmissions are organized into frames into a 10ms frame as shown below:

Where:

The frame consists of 10 subframes of 1 ms each.

Slots

Just like LTE, a slot is always 14 symbols. The number of slots in a subframe depends on the numerology μ.

Symbol level TDD

5G slots support symbol level TDD formats. Each symbol can be designated as:

D: Downlink
U: Uplink
X: Flexible

UE assumes that downlink reception can take place only in symbols marked D or X in the following table.

Similarly, the UT can transmit in the uplink only in slots marked U or X.

Symbol level slot configuration (D: Downlink, U: Uplink, X: Flexible)

TS 38.212: Multiplexing and channel coding

The scope is to describe the transport channel and control channel data processing, including multiplexing, channel coding and interleaving, and to specify:

Channel coding schemes
Rate matching
Uplink transport channels and control information
Downlink transport channels and control information

Channel coding

5G NR traffic channels are encoded using the LDPC (Low Density Parity Check) coding. Control channels are encoded with the Polar codes.

Modulation schemes

5G-AN supports 1 to 8 bits per symbol (Q).

Downlink Control Channel (DCI) formats

A DCI transports downlink and uplink scheduling information, requests for aperiodic CQI reports, or uplink power control commands for one cell and one RNTI.

DCI format 0_0 is used for the scheduling of PUSCH in one cell.
DCI format 0_1 is used for the scheduling of PUSCH in one cell.
DCI format 1_0 is used for the scheduling of PDSCH in one DL cell.
DCI format 1_1 is used for the scheduling of PDSCH in one cell.
DCI format 2_0 is used for notifying the slot format.
DCI format 2_1 is used for notifying the PRB(s) and OFDM symbol(s) where UE may assume no transmission is intended for the UE.
DCI format 2_2 is used for the transmission of TPC commands for PUCCH and PUSCH.
DCI format 2_3 is used for the transmission of a group of TPC commands for SRS transmissions by one or more UEs. Along with a TPC command, a SRS request may also be transmitted.

TS 38.213: Physical layer procedures for control

The scope is to establish the characteristics of the physical layer procedures for control, and to specify:

Synchronization procedures
Uplink power control
Random access procedure
UE procedure for reporting control information
UE procedure for receiving control information

Cell search and timing adjustment

The cell search and timing adjustment procedures have been enhanced to work for 15 KHz to 240 KHz subcarrier spacing.

Power control

The power control scheme has also been extended to work for all numerologies. The 2^μ term in the PUSCH power calculation factors in the different numerologies.

TS 38.214: Physical layer procedures for data

The scope is to establish the characteristics of the physical layer procedures for data, and to specify:

Power control
Physical downlink shared channel related procedures
Physical uplink shared channel related procedure

Downlink MCS index table

The downlink MCS index table specifies the modulation, coding and the overall spectral efficiency of the PDSCH.

Uplink MCS index table

The uplink MCS index table specifies the modulation, coding and the overall spectral efficiency of the PUSCH.

Downlink CQI reporting

The UE reports downlink CQI via a 4-bit field that is carried over the PUCCH or the PUSCH. Two different tables are defined.

CQI reporting limited to 64-QAM

CQI reporting extended to 256-QAM

CQI reporting table (extended to 256-QAM)

TS 38.215: Physical layer measurements

The scope is to establish the characteristics of the physical layer measurements, and to specify:

Control of UE/NG-RAN measurements
Measurement capabilities for NR

5G NR physical layer introduction

The following video provides a good overview of the 5G NR physical layer. The topics covered are:

Waveforms and frame structure

Scalable numerology
Numerology multiplexing
Dynamic TDD

Millimeter waves

Beam sweeping
Beam management
Massive MIMO

Low latency

Mini slots
CBG (code block group) retransmission
Front loaded DMRS (demodulation reference signal)

Understanding the 5G NR physical layer (slides)

September 26, 2018/by najeebgafar@gmail.com