Antcor S.A. - LteWave - An application used for the generation of LTE-compliant waveforms

LteWave

A stand-alone application used for the generation, visualization and analysis of LTE-compliant waveforms. LteWave can display a large amount of information on the LTE signals generated according to user-specified parameters. The output is visualized in terms of the resource grid, constellation diagrams, time-domain waveforms, frequency-domain spectrum, channel estimation and power-delay-profile of the channel. With a clear and user-friendly interface the effect of the wireless channel and signal processing on the transmitted and received LTE signals can be easily investigated.

The following paragraphs give an outline of LteWave’s system requirements and graphic user interface. The main functionality of the software along with known limitations are also discussed.

System requirements

LteWave requires a PC running Windows XP / Vista / Windows 7 operating system and MATLAB Compiler Runtime (MCR).

LteWave Interface

The main LteWave interface window is composed of the 4 items indicated below (click for more details):

1. LteWave toolbar
2. Waveform parameters input table

Waveform parameters input tableIn the waveform parameters input table the user can select a number of eNodeB/channel-related parameters which affect the transmitted/received waveforms. In detail, the input table contains the following entries:

eNodeB
- Subframe number – Subframe of interest according to [1].
- Symbol number – OFDM symbol number of interest according to [1]. This field takes values between 0 and 13 for normal cyclic prefix and 0 to 11 for extended cyclic prefix.
- Tx bandwidth – Transmit bandwidth configuration as defined in [2].
- CQI – Channel Quality Indicator value for PDSCH corresponding to a specific modulation and coding parameters as defined in [3].
- CP length – Cyclic-prefix length of the OFDM symbols as defined in [1].
- CFI configuration – Length of control region according to [4]. Note: At the lowest bandwidth configuration setting (1.4 MHz) the number of OFDM symbols for control region is CFI + 1.
- PAPR target – Specifies a target Peak-to-Average Power Ratio. This is achieved by performing PAPR clipping in the time-domain waveform. Note: In order for a new value to be committed the ENTER key needs to be pressed after any alteration in the value of this field.
Channel
- SNR – Desired Signal-to-Noise Ratio (in dB) of received signal. Note: In order for a new value to be committed the ENTER key needs to be pressed after any alteration in the value of this field.
- Channel type – Channel model selection from the following [5]:
  - AWGN – Additive White Gaussian Noise model
  - EPA – Extended Pedestrian A model
  - EVA – Extended Vehicular A model
  - ETU – Extended Typical Urban model

3. Measurements information box

Measurements information boxThe measurements field contains information regarding the transmitted and received signals as well as the channel model. In detail, the following information is displayed:

Transmitter
- Useful bandwidth – Corresponds to the bandwidth occupied by the active subcarriers.
- EVM – The Error-Vector-Magnitude is a measure of the accuracy of the constellation points. At the transmitter, an EVM value above 0% is attributed to imperfections from PAPR clipping.
- Original PAPR – Corresponds to the Peak-to-Average Power Ratio of the time-domain signal before PAPR clipping.
- Clipped PAPR – Corresponds to the Peak-to-Average Power Ratio of the time-domain signal after PAPR clipping. Note: This value is usually slightly different from the target PAPR required since any clipping of the signal’s peaks affects also the average power.
Channel
- RMS Delay Spread -Root-Mean-Squared delay spread of the Power Delay Profile of the wireless channel chosen.
Receiver
- EVM – EVM value at the receiver. This value is further increased (from the transmitted EVM) due to inaccuracies in the channel estimation and the existence of AWGN noise.
- Estimation RMSE – Root-Mean-Squared-Error of the estimated channel response with respect to the actual response.
- BER – Uncoded (i.e. not taking any error-correction into account) Bit-Error-Rate of the received PDSCH data.
- Block Error – A true / false indicator corresponding to the CRC check of the PDSCH transport block.
- Throughput – Data throughput for the PDSCH channel in Mbits per second.

4. Plotting area

Plotting areaThe main plotting area is used for the display of the plots corresponding to the buttons in the LteWave toolbar.

Resource grid – Depicts the resource elements utilisation in terms of the broadcast, control, reference, synchronisation and PDSCH (user data) channels according to [1].
Constellation diagram – Displays the In-phase and Quadrature components of the modulated transmitted/received signal. The ideal modulation points are also plotted for reference. The transmitted symbols are only impaired by any potential PAPR clipping applied to the transmit waveform. The received symbols (after equalisation) are impaired by AWGN noise and imperfections of the channel estimation process.
Time-domain waveform – Displays the real, imaginary and absolute values of the transmitted waveform for the 1 subframe (duration = 1 ms).
Frequency-domain signal – Displays the transmitted and received signal spectrum. The transmitted signal ideally has a square spectrum and is only impaired by potential PAPR clipping applied to the transmit waveform. If no PAPR clipping is applied to the signal, the noise floor (around -300 dB) of the transmitted spectrum is due to the Matlab accuracy limits.
Channel estimation – Displays the channel response of the useful bandwidth along with the estimated channel. The latter is impaired by the limited resolution of reference symbols and the existence of AWGN noise.
Power Delay Profile – Displays the Power-Delay-Profile (PDP) of the wireless channel in terms of the relative delay and power components of multipath. In the case of AWGN channel, the PDP consists of a single component of power equal to 30 dBmW (1 Watt).

Undock Button On the top-right section of the plotting area an “Undock” button is provided. This enables the extraction of multiple figures from the main plotting area to individual figures which can then be saved, printed or exported. Note: Figures undocked from the main plotting area do not refresh when a new waveform is generated. The users can utilise this feature for comparing figures corresponding to different waveforms (eg compare the constellation diagrams for SNR = 10 dB and SNR = 20 dB).

Known limitations and future releases

The LteWave software has currently limited functionality in terms of the supported transmission modes, importing/exporting of user data, channel models and signal impairments. Future versions are designed to address these issues but in the meantime any feedback will help us prioritise the potential extensions to this application.

References

[1] – 3GPP TS 36.211 v8.9.0 – Physical Channels and Modulation
[2] – 3GPP TS 36.104 v8.8.0 – Base Station (BS) radio transmission and reception
[3] – 3GPP TS 36.213 v8.8.0 – Physical layer procedures
[4] – 3GPP TS 36.212 v8.8.0 – Multiplexing and channel coding
[5] – 3GPP TS 36.101 v8.8.0 – User Equipment (UE) radio transmission and reception

Downloads

An evaluation version of LteWave is available for download here. The commercial version incorporates save/load functionality of the input data and output waveforms.