Spread Spectrum Based Jpeg Image Transmission Computer Science Essay

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Advantages of Spread Spectrum technology is well established in wireless mobile communication. This coded technology could be used for image transmission in a dynamic channel condition. This work efforts to simulate JPEG image transmission in Dedicated Short Range Communication for Intelligent Transportation System using Spread Spectrum based transmitter and receiver in base-band. Matlab/Simulink platform is used for the simulation. Successful reception of the image is shown even in the worst channel condition.

In recent years, wireless multimedia communication systems have become increasingly popular as an inexpensive and promising means for ubiquitous and wireless communications. The demand of Multimedia services is growing for wireless systems. Modern consumer electronics applications demand robust wireless communication schemes for effective performance [1,2]. Due to the rapid growth of mobile wireless communications systems, there has been an increasing demand for wireless multimedia services like image and video transmission, speech and data transmission. The wireless image transmission is expected to become a breakthrough application for the successful commercial development of wireless communication systems. Image transmission is one of the future potential multimedia services which should be supported with a high wireless transmission bit-rate within a ample bandwidth and require efficient error free and high speed communication systems. Wireless sensor networks are an enabling technology for many future applications, but still it is not sufficient for multimedia system[3].

Today airwaves are too crowded that some bands are so overloaded that long waits and interference are the normal. The availability of these transmission links depends on the wireless systems in use. Thus due to limited radio spectrum, only a finite number of radio communication channels can be shared by mobile users. As a result, image data should be compressed before transmission in order to efficiently use each radio channel. Again, atmosphere is the main constraint to achieve high speed data communication [4]. Recent studies have shown that high data rate is possible only under favorable conditions like near the base station and no other users competing for bandwidth [5]. In a multiuser environment the wireless transmission performance is fundamentally limited by interference due to the presence of signals from other users as well as from multipath. Specially, the performance of wireless communication systems is limited by time dispersion in the channel as a result of multipath. Dispersion gives rise to frequency-selective fading which results in a distorted frequency spectrum of the information signal [6]. It is usually assumed that the multipath delay spread is smaller than a symbol duration [7] because larger values of delay spread cause significant intersymbol interference (ISI), which limits the achievable data rate. Fading, Jamming, Security are also the importtant issuses in wireless communication. Proper channel study is required for designing a good communication system.

Channel impairments oppose the data rate enhancement in wireless communication. In many applications such as wireless local area networks (WLAN) and indoor radio, the received signal contains components that have traveled from the transmitter to the receiver via multiple propagation paths with differing delays; this phenomenon is called multipath propagation and [8,9]. Multipath is more effective at high speed moving vehicle and high data rate as shown in Fig. 1. [10]. The multiple copies of a symbol interfere with the multiple copies of the previous symbol at high data rate. But if the data rate is sufficiently low then the probability of the interference is less. But for multimedia application higher data rate is required.

Dedicated Short Range Communication ( DSRC ) :

Dedicated Short Range Communication (DSRC) [11], standard being promoted by the Intelligent Transportation Society of America and the United States Department of Transportation for short range communication in Intelligent Transportation System (ITS). A number of wireless solutions were evaluated for use as the primary communication medium for DSRC [12] which enables a new class of communication applications that will increase the overall safety and efficiency of the transportation system.

In first generation, DSRC was used for toll collection system operates at 915 MHz and has a transmission rate of 0.5 Mb/s. The Federal Communication Commission (FCC) [13] allocated the 75 MHz of bandwidth in the 5.9 GHz band for the second generation of DSRC. Since the allocation of the bandwidth, standardization bodies have been working on the implementation details of 5.9 GHz DSRC. To reduce the traffic hazards, the North American DSRC standards program aims at creating an interoperable standard for use in the US, Canada, and Mexico. 5.9 GHz DSRC spectrum is composed of six service channels which are each 10 MHz. Also, one control channel is provided by the DSRC standard, which is also 10 MHz and FCC recommends no unlicensed use of DSRC band. Fig. 2. provides the channel layout for DSRC.

The 902-928MHz band is full of traffic. Other devices that occupy the band are 900 MHz phones, rail car AEI readers, and wind profile radars. A number of wireless solutions were evaluated for use as the primary communication medium for DSRC [14]. In addition, the wireless technology must support a number of diverse communication schemes[11].

Spread Spectrum Technology :

In order to support high data rate multimedia application the Code Division Multiple Access (CDMA) plays an important role in wireless communication. CDMA is an well established method for multiple access and interference cancellation technique [15] based on Spread Spectrum (SS) technology which was first seriously elaborated on by Salmasi and Gilhousen in the year 1991 [16]. The SS technology as well known for its antijamming and security [17,18,19] features was initially developed for military and intelligence requirements [20].

The third-generation (3G) and fourth-generation (4G) mobile communications are expected to provide a high-rate data services [21]. WCDMA (Wideband Code Division Multiple Access) is the dominant transmission technology for 3G and OFDM (Orthogonal Frequency Division Multiplexing) becoming very popular and other evolving technology is UWB (Ultra Wide Band). However, keeping in mind the spectral limitation as an effort to support such high rates, the multiple antennas [22] and multiuser detection algorithms [23] are used for the performance improvement in the DS-CDMA systems.

SS Based Image Transmission :

Spread Spectrum has great potential as a communication scheme for consumer electronic applications as it has a very high capability of providing security, anti-jamming and multiple access facilities. The direct-sequence signaling is accomplished by multiplying the data signal with a pseudorandom sequence. The greater the length of pseudorandom sequence, the higher is the level of security. Recently, researchers are trying to transmit of DPCM-coded and layered images via radio multipath fading channels with TDMA QAM or QDPSK modulation [24,25]. JPEG developed a new kind of technology which referred to as JPEG 2000 Wireless (JPWL) [26,27] to achieve efficient transmission of JPEG 2000 images over an error-prone wireless transmission environment.

An energy efficient JPEG 2000 image transmission system over point-to- point wireless sensor networks proposed by [28,29] proposed a scheme of multiple bitstream image transmission over wireless sensor networks, it used multiple bitstream images encoding to achieve error robust transmission and small fragment burst transmission to achieve efficient transmission. [30,31] gives different method of distributed JPEG2000 Image Compression for Sensor Networks. Our literature survey reveals that very little work has been done for image transmission by employing the well-known spread-spectrum techniques. While moving in a high speed car in an urban area, the use of spread spectrum can reduce the effects of multipath, i.e it can increase the mobility of the multimedia terminals.

Image Transmission :

We are successful to simulate SS based JPEG image transmission in MATLAB/SIMULINK platform. Details of the SS system is discussed below.

Transmitting Section (Tx):

The details block diagram of the transmission system is shown in Fig. 3. The SS system selects the source image (JPEG) and then it is converted to a gray image by discarding its color component for simplicity of process. This image is the compressed using the discrete cosine transform block and undergoes a data type conversion to unit8. Using a reshape block the image matrix is then converted into a column vector. This column vector undergoes an integer to bit conversion for being transmitted through the SS system.

Receiver Section (Rx) :

In the receiver section (Fig. 4) we try to reform the image from the data obtained from the transmitted section. The received data-bit(Rx) is converted to integer. Reshape block converts the data obtained in column vector to the original matrix transmitted. We compare the Rx and Tx matrices and then perform the data type conversion of the obtained data from integer to double. The Inverse Discrete Cosine Transform (IDCT) block decompresses the data and helps us to obtain the original image. The Tx and Rx image are shown in Fig. 5. and Fig. 6. respectively.

Novelty of the Work

DSRC is standardized for vehicular communication. DSRC is based on IEEE 802.11a which supports 54 mbps data rate. Thus by using spread-spectrum in the base band and DSRC as air interface, error free image transmission is possible even in a multipath scenario.

It is already mentioned that in section-III that our literature survey reveals that very little work has been done for image transmission by employing spread-spectrum techniques. Wong et al. [32] has presented a spread spectrum based image transmission method for an indoor WLAN. But neither WLAN standard used is mentioned nor is the quality of received image shown. Further the type of image transferred is also not mentioned. In the present work we have simulated the “*.jpgâ€Â image transmission and the received image is shown. This work is exclusively suitable for transmission through IEEE 802.11a based WLAN radio networks. DSRC is such kind of system and hence the spread spectrum based image transmission is possible in vehicular communication.

CONCLUSION

The transmitting and receiving section for image transmission was modeled as shown in the block diagrams above. We are successfully able to retrieve the original image transmitted in the form of bits at the receiving section. The higher data rate as well as range of DSRC system can be achieved incorporating SS system. However, this transmission and reception section yet not been implemented in hardware platform. We are now working for Software Defined Radio (SDR) implementation of SS based DSRC system for multimedia applications in ITS.

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