Performance of LTE downlink communication system in presence of electronic warfare spot jamming

Wireless communication is one of the principally active zones of tools development and has become necessary part of everyday life. Simulation of wireless communication systems accurately is very important for predicting its performance under different scenarios. Long-Term Evolution (LTE) is named by next generation wireless communications. It is a standard for high-speed wireless communication for mobile phones and data terminals. In this paper, the performance of standard single-input-single-output (SISO) LTE Frequency Domain Duplex (FDD) downlink (DL) signal in additive white Gaussian noise (AWGN) channel is evaluated in two scenarios without jamming and in presence of electronic warfare spot jamming. Firstly, the performance of the standard LTE communication system in absence of jamming is investigated by calculating the probability of Bit Error Rate (BER) and Frame Error Rate (FER) versus Signal Noise Ratio (SNR). Secondly, the performance in presence of electronic warfare spot jamming scheme is investigated by constant Jamming to Signal Ratio (JSR) and different values of the normalized jamming bandwidth. In order to illustrate the impact of jamming on the standard LTE DL wireless communication system, the measurement is evaluated by using the aid of SystemVue software program.


Introduction
Long Term Evolution has long been seen as the primary development to reach a stronger, faster wireless communications systems. The data rate of communication systems under LTE can currently reach peak downlink rates of 100Mbps and uplink speeds of 50Mbit/s. The transmission of downlink LTE signals has been based on Orthogonal Frequency Division Multiple Access (OFDMA) [1] and uplink transmission has been based on Single Carrier Frequency Division Multiple Access (SC-FDMA) [2].
Synchronization sequences are used in LTE downlink signal for new cell identification and initial synchronization. A robust primary synchronization signal sequence detection algorithm is explained in [3]. Problems related to time and frequency synchronization as well as blind Cyclic Prefix (CP) type identification in 3GPP LTE system is discussed in [4]. The work in [5] compares the complexity, latency, and recognition probabilities of frequency and time domain LTE physical layer identity detection schemes.
The performance of a LTE communication system can be deteriorated due to the presence of another high power in band communication services or due to the intended jamming signal. In [6], the work investigated the problem of optimal jamming technique over an AWGN channel against digital modulation communication schemes (OFDM). In [7], the performance of multiband OFDM ultra-wideband communication system was investigated in presence of in band OFDM-based WLAN interference. In order to participate in this interesting field of study .In this paper, the performance of the standard LTE communication system is investigated in presence of electronic warfare spot jamming technique in AWGN channel. This investigation is held by

OFDM technique
The LTE communication system is design bases of a very complex system because of the requirements that can be represented by high peak transmission rate (100 Mbps DL/50 Mbps UL), multiple channel bandwidths (1.4, 3, 5, 10, 15 and 20 MHz) and spectral efficiency. To achieve these requirements, orthogonal frequency division multiplexer (OFDM) has been chosen to be the basis of LTE communication system. Figure 1, depicts the LTE OFDM transceiver block diagram. The intersymbol interference (ISI) is mitigated by using cyclic prefix (CP). The second advantage for using OFDM technology was converted the frequency selective fading that destroyed the mobile signal to flat fading seen by each sub-carrier.

Physical layer parameter
The LTE physical layer downlink is based on OFDMA. OFDMA has two main problems. The first problem is high peak-to-average power ratio (PAPR) and the second problems is high sensitivity to frequency offset. There are two different modes of operation in building LTE downlink signal. The two modes of operation are frequency domain duplex (FDD) modes and time domain duplex (TDD). In this paper, the FDD mode is selected.
In the time domain, the OFDM symbol period equals (1/30720000).Subcarriers are collected in 180 kHz blocks, each block consists of 12 subcarriers. In case of normal cyclic prefix, every 0.5 ms slot in length ( = 15360 ・ ) 7 consecutive OFDM symbols have been transmitted and 6 in case of the extended cyclic prefix. The frame in length ( = 307200 ・ ) is consisted of 10 subframes in length (Tsubframe = 30720 ・ ) and subframe is consisted of two slots. The LTE frame structure in FDD is represented in Figure 2.  Figure 2. The LTE frame structure in FDD mode, f = 15 kHz. All the symbols transmitted in a single slot on all subcarriers in a block form a Resource block (RB) which consists of 180 kHz, for the duration of one slot (0.5 ms), or 12 consecutive sub-carriers. A Resource element (RE) is the smallest defined unit that consists of one OFDM sub-carrier during one OFDM symbol interval. As shown in Figure 3, some resource elements are used for special purposes like as, Reference signals(RS), Primary Synchronization Sequence (PSS), Secondary Synchronization Sequence (SSS)., control signaling, and critical broadcast system information. The data transmission has been used the remaining.
In case of normal CP, Each RB consists of 12 ・ 7 = 84 (RE). In case of extended CP, Each RB consists of 12 ・ 6 = 72 (RE).

Jamming techniques
Wireless communication system facilities the communication among peoples and exchanges the data. In the military field, it has additional function which investigated in control the leader its forces and give them orders and information. The field work for accomplish the intercept or denial of communications is named by Electronic Warfare (EW). Jamming is one way to disconnect between Wireless communications systems. It has several techniques, like, Barrage Jamming, Spot Jamming, Tone Jamming, Pulsed Jamming and Smart Jamming. Barrage jamming is named by Broad Band Jamming (BBJ). It spreads jamming signal power (J) over all the band of transmitted signal (Wss). Jamming power spectral density (Nj) is given by In case of Partial Band Jamming (PBJ) or Spot, jamming, jamming signal power spreads on a partial of transmitted signal band (Wss). The bandwidth of jamming (Wj) is less than the transmitted signal bandwidth. The ratio between the jamming bandwidth and transmitted signal bandwidth is defined by = ≤ 1 The jamming technique that concentrate more jamming power on a fraction of the transmitted bits denoted by Spot jammers. This concentration can cause high error probabilities comparing with that broadband jammer. In this paper, we are concerned about the Spot Jamming technique. Jamming power spectral density (N ' j) is given by

Definition
Keysight SystemVue software is a powerful, electronic system level (ESL) design environment.
The physical layer (PHY) of wireless communication systems can architected by using SystemVue software. It provides unique value to RF, DSP and FPGA/ASIC implementers who rely on both RF and digital signal processing to deliver the full value of their hardware platforms that adhere to the PHY of modern emerging standards.

Design circuit
The practical environments can be simulated by using tools that have been designed on SystemVue software. Figure 4, shows the schematic for transmitter and receiver of downlink SISO LTE signal and EW Jamming. This schematic is used for measurement of the both Bit error rate (BER) and Frame error rate (FER) on (AWGN) channel for different modes of operation (with respect to the jamming).  The used block can be classified as:

Transmitter
The transmitter of downlink SISO LTE signal consists of several simulated blocks shown in Figure 5. Every block has its own function, as follow.

a) Source block
It generates the pattern data, where pseudorandom sequence (PN9) was used. This random sequence generates a 511-bit pseudo-random test pattern.

b) LTE downlink signal source block
In this block the downlink LTE signal with frame mode (FDD) is generated. The used cyclic prefix (CP) mode is normal, with band width (BW) [5MHZ], and using QPSK modulation.

c) CxToRect block
CxToRect converts input complex values to output real and imaginary values.

d) Oscillator block
It's generates carrier signal with defined value of amplitude, phase, and carrier signal frequency.

e) Modulator block
The modulator block performs different modulation schemes such as, amplitude, phase, frequency, or I/Q modulation signals. This occur at defined carrier frequency according to the carrier frequency generated by the oscillator block.

Channel
The second step on our work is to design the AWGN channel. The block in Figure 6 generates the AWGN channel.

Receiver
The receiver of downlink SISO LTE signal consists of three blocks shown in Figure 7. Every block has its own function, as follows.

c) LTE_DL_Receiver block
It recovers back the original data which be the input of the downlink LTE signal source. This block is depended on the priori information of downlink LTE signal source parameters. These parameters are frame mode (FDD), cyclic prefix mode (normal), transmitted signal bandwidth [5MHZ], and modulation type (QPSK).

EW Jamming
The EW Jammer consists of two blocks as shown in Figure 8. Every block has its own function, as follows.  The impact of Jamming signal on the LTE DL signal is measured by the probability of Bit Error Rate (BER) and Frame Error Rate (FER) versus Signal Noise Ratio (SNR) and depicted in Figure 12 and Figure 13 respectively.
It can be seen in Figure 12 that the presence of jamming signal can easily degrade the performance of the slandered LTE communication signal. As shown at BER equals to10 −4 , a SNR degradation of nearly 7 (dB) for the LTE BER performance in presence of EW spot jamming with BW equals to 0.6 MHZ (12% of the LTE BW is jammed) and BW equals to 2.4 MHZ(48% of the LTE BW is jammed).  Figure 13, it can be seen that also, the FER of the slandered LTE communication system is degraded due to the presence of EW spot jamming signal. It can be seen that at FER equals to10 −5 , a SNR degradation of nearly 8 (dB) is achieved if the jamming bandwidth is increased from 0.3 MHZ (6% of the band) to 2.4 MHZ (48% of the band).

Conclusion
The topics investigated in this paper are important when the presentation of LTE air interface for public safety communication is considered. The performance of LTE DL SISO communication system was simulated by the aid of keysight SystemVue software in presence of EW spot jamming in AWGN channel. The results show that the performance of LTE Downlink communication system was decreased by the presence of EW spot jamming. The performance was evaluated by measuring the Bit Error Rate and Frame Error Rate of standard LTE DL communication system against Signal to Noise Ratio in presence of EW spot jamming signal at fixed SJR equals to 0 (dB). The results also show that increasing the jamming bandwidth increase the amount of performance degradation.