Design of Future Software Defined Radio (SDR) for All-IP Heterogeneous Network

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12 Recent Patents on Signal Processing, 2010, 2, Open Access Design of Future Software Defined Radio (SDR) for All-IP Heterogeneous etwork Md. Zahangir Alam *,1 and M. Abdus Sobhan *,2 1 Electronic
12 Recent Patents on Signal Processing, 2010, 2, Open Access Design of Future Software Defined Radio (SDR) for All-IP Heterogeneous etwork Md. Zahangir Alam *,1 and M. Abdus Sobhan *,2 1 Electronic and Telecommunication Engineering Department, Prime University, Dhaka, Bangladesh 2 School of Engineering and Computer Science (SECS), IUB, Dhaka, Bangladesh Abstract: The software defined radio (SDR) is the heart of the 4G mobile communication to access any network at any time basis. The different wireless networks such as cellular, codeless, wireless local area network (WLA) having different band of frequency requires individual software to access any call. The SDR device requires more antennas and low noise amplifier (LA) because it is impossible for single antenna and single band pass filter to operate at all the frequency bands. Large number of antennas, filter and amplifier increased the size of the device. The SDR scan the available network and download the required software from WLA, memory card, PC server etc. The downloading creates some problem, such as the limited download speed and its reliability. In this paper, the authors study the architecture of SDR based on the recently proposed CI-OFDM multiplexing technique to operate all networks in a particular band-width. We also find the interference among different CI channels of the same and different networks. Finally, we discuss the calling procedure between one user of one network and another user under another network using IP address. Keywords: SDR, OFDM, heterogeneous network, 4G, CI-OFDM. I. ITRODUCTIO The first public mobile telephone system known as Mobile Telephone System (MTS) was introduced in United States in To provide higher capacity, the cellular concept is introduced in which the operating area of the system was divided into a set of adjacent, non-overlapping cells. The first generation (1G) of cellular system supported the analog cell phones with the speeds up to 2.4 Kbps. To support digital signal, the second generation (2G) system was planned with speeds up to 64 Kbps. To meet the future bandwidth hungry services, the third generation (3G) wireless system was developed in 1990s, which provided the transmission speeds from 125 Kbps to 2 Mbps. Future of the mobile communication (Beyond 3G) will be towards an integrated system (Heterogeneous etwork) which will produce a common packet switched, possibly IP-based, system to access different types of networks by a single user terminal. The fourth generation (4G) is a high speed wireless network that transmits multimedia and other data over the wire-line backbone network [1]. Future mobile communications will provide seamless services comprising IP-based network that supports seamless interoperation between different networks. The IP network provides a seamless global roaming service through inter-system handover designed to enable handover between terminals using different technologies and of different bandwidths and *Address correspondence to these authors at the Electronic and Telecommunication Engineering Department, Prime University, Dhaka, Bangladesh; School of Engineering and Computer Science (SECS), IUB, Dhaka, Bangladesh; Tel: ; Fax: ; frequencies [2]. To achieve this goal, vertical handover technology and SDR technologies are needed. The IP-based 4G heterogeneous networks provide data and multimedia services by an integrated terminal at any time and anywhere basis. The 4G networks provide higher data rates with significant reduction of interference at the receiver caused by the multi-path propagation through the channel, which targets the market of 2010 and beyond. About 84% of all mobile phone subscribers in Japan have upgraded from slower 2G mobile services to 3G for higher data rate. Around 2010, The Japanese mobile operators will introduce Long Term Evolution (LTE) , services which are sometimes termed 3.9G or Super-3G. The 4G technologies are currently under development and testing. 4G services will be introduced to the markets in Japan around 2015 or later. TT DoCoMo introduced the next generation of mobile communication technology in 2002, which has been called 4G (fourth generation). Samsung Electronics Co. Ltd. demonstrated 4G mobile technology at the annual Samsung 4G Forum in Korea with the data rate up to 60 Mbps in motion and 100 Mbps in stationary case. The 4G framework provides high speed wireless network that can transmit multimedia information with the required data rate. The problem to access different networks by an integrated user terminal is [3], a) it is impossible to have just one antenna and one LA to serve the wide range of frequency bands and b) the slow downloading problem. To access different networks by a single user terminal, software radio receiver is proposed as in [4], in which a two dimensional CI-OFDM codes are assigned. The first dimensional CI-code is for the desired user and the second dimensional one is for the network in which the user is assigned. As a result, each antenna and amplifier accesses the whole frequency band as in OFDM technology according / Bentham Open Design of Future SDR for All-IP Heterogeneous etwork Recent Patents on Signal Processing, 2010, Volume 2 13 to the patent [5]. The contribution of the proposed system as in [4] is that single antenna and LA can be designed to access all networks and users of each network by using two dimensional CI-codes in which each network and each user can be identified by corresponding CI-code. The two dimensional which is used to multiplex different network and CI-OFDM requires the same bandwidth as OFDM but the s provide different phase shift to different sub-carriers [6]. Hence all devices such as LA and filter operate in the same band for all networks. In this paper, the authors attempt to discuss the architecture of SDR depending on the recent proposal to access any network by using single antenna and LA through. The capacity of the cellular system under single network and multiple networks is calculated. The cell structure for CI/OFDM based cellular system is discussed in this paper. The interference of different channel having individual CI-codes under the same network and different networks are calculated in terms of carrier to interference ratio (CIR) in the hexagonal cellular wireless system. Each network is identified by the sub-carrier frequency of OFDM symbol and the user channel is identified by CI-codes, while in GSM system, different channel has different frequency band and in CDMA system, different channel has different spreading (P) codes. Finally the calling procedure between one user of one network and another user under another network is discussed using the carrier frequency of that particular network and the corresponding of those users. II. WHY 4G? The main driver for 4G is data rate without any loss of user data after transmission through a noisy channel. 4G is a wireless link that provides very high data rate through a fading channel at data rate of 100 Mbps in moving environment and 1 Gbps in stationary condition. The development of integrated wireless network in 4G enables to connect several present and future wireless access technologies such as WLA and cellular technologies like UMTS, EDGE, etc., and seamlessly move between all the networks under 4G platform using IP based wireless technology. 4G is developed to provide high data rate according to different user access networks such as wireless broadband access, Multimedia Messaging Service (MMS),Teleconferencing, video chat, mobile TV, IPTV, HDTV content, Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB) etc. The IP based 4G wireless heterogeneous system provides a new air interface that provides seamless operation with higher data rates with minimal error using OFDM based multiplexing technology. Basically, the 4G system accesses any types of network and provides a comprehensive IP solution based on Internet Protocol version 4 (IPV4), or Internet Protocol version 6 (IPV6), where voice, data and streamed multimedia can be given to users demands using OFDM technology. III. SDR APPROACH The SDR is a communication system that integrates different types of network in a common platform. It uses appropriate software for modulation and demodulation of the radio signals assigned to each network. The SDR produces a radio link that can receive and transmit a new form of radio protocol by running the particular software. The SDR consists of a super-heterodyne RF section to convert RF signals to analog IF signals, and analog to digital converter and digital to analog converters which are used to convert a digitized IF signal from and to analog form [7]. The SDR technologies provide different technologies such as interference management and capacity enhancement over a broad frequency spectrum, with ensuring secure communications management. IV. SIGAL RECEPTIO THROUGH SDR SDR is the main device for a user terminal to access different network using individual IP address. Fig. (1) shows the design of an ideal software radio to access different networks [7, 8]. It consists of mainly two parts, one analog part and another digital part. The transmitted analog high frequency signal is down converted to lower frequency by super-heterodyne principle. The analog part consists of an antenna, a band-pass filter (BPF), and an LA. At the digital part, the received analog signal is digitized by the analog to digital converter (ADC) immediately after the analog processing. The modulation, coding, security and other processing are performed in the next stage by a reprogrammable base-band digital signal processor (DSP). The problem of SDR is to access the whole bandwidth for all networks; because one antenna and one LA cannot serve the wide range of frequency bands. To access the entire network the only solution is to use multiple analog parts to work in different frequency bands. This solution increases the design complexity and physical size of the terminal. Fig. (1). An ideal software radio receiver [3]. V. SOFTWARE DOWLOADIG Multimode user terminals should be able to select the target wireless systems. This process becomes complicated in 4G heterogeneous systems [8]. One of the solutions is to use software radio device that can scan the available network and load the required software and reconfigure themselves for the selected networks. Fig. (2) shows the attachment process of multimode terminal to a WLA, which scans the available wireless networks, and after scanning, it downloads the required software. The software can be downloaded from the media such as a PC server, Smart card, or memory card, or over the air (OTA). As pointed out in [6], we still need to solve problems such as the deleterious, low downloading speed. VI. OFDM BASICS OFDM is the driving force of 4G wireless communication and is used in 4G with integrated WiMax to 14 Recent Patents on Signal Processing, 2010, Volume 2 Alam and Sobhan provide higher data rate and large coverage area. OFDM also increases the spectrum efficiency. OFDM is based on a mathematical process called the Fast Fourier Transform (FFT), which provides the wireless channel to overlap without losing their individual characteristics (that maintain orthogonality between the sub-carriers). This provides efficient use of the spectrum and enables the channels to be processed at the receiver more efficiently. In OFDM, an incoming high data stream enters at the transmitter side. As seen in Fig. (3a), this incoming data is converted into serial to parallel form, the frequency domain data stream is converted into time domain by IFFT, and carrier spacing is carefully selected to ensure orthogonality between all subcarriers.. It can download suitable software manually or automatically [8]. and (2) to resolve the channel s multi-path profiles. The CI signal is- Denoted by c(t) and consist of carriers in phase, each equally spaced by frequency separation f. A frequency sampled with phase offset from carrier to carrier of the sinc(x) waveform. An approximation to the sinc(x) waveform generated by frequency sampling the sinc(x) waveform using equally spaced samples. Fig. (2). A multimode terminal attached to the WLA that scans the available networks [9]. Fig. (3a). OFDM Transmitter. Mathematically, the transmitted signal can be written as [10]: S(t) = X k e j 2 f kt ;t = [0,T ]. (1) k=0 where, X k, is the modulated complex data symbol and f k is sub-carrier frequency, and T is symbol period. At the receiver side, the incoming data stream is first returned to base-band by using the same sub-carrier frequency that is assigned to the transmitter. After converting the analog signal into digital, the cyclic prefix is removed. The serial data is then converted to parallel and a simple decision device is applied. Receiver implementation can be greatly simplified by use of an FFT to get the original transmitted symbol. The OFDM receiver structure is shown in Fig. (3b). VII. CI/OFDM APPROACH The OFDM is a multi-carrier system, where an incoming high data stream is mapped to low rate stream and the carriers are combined together and sent out over the channel. In CI approach [6], at the heart of Carrier Interferometry technology lays the signal referred to as the Carrier Interferometry (CI) signal. The CI signal is very narrow, enabling it (1) to be easily separated from other CI signals, Fig. (3b). OFDM receiver. A CI signal positioned with a main-lobe centered at time 0 is orthogonal to a CI signal with its mainlobe positioned at time, where is a value in the set {k/(f), k=1,2,.- 1)}. This property assures that CI waveform can be applied to represent information symbols located sequentially in time, without creating inter-symbol interference. VIII. OVEL MULTIPLEXIG TECHIQUE TO ACCESS HETEROGEEOUS ETWORK A number of antennas and Band pass filters (BF) are used at the Base Station (BS) to access different networks such as GSM, GPRS, CDMA, UMTS, and WLA etc. Multiple analog parts are used in SDR to work in different frequency bands because each analog device is designed to work in a particular frequency band. The multiple analog parts increase the design complexity and physical size of the terminal, and decrease the switching time. The SDR device selects the target wireless systems by scanning the available network. Each network has unique software to process each call and the SDR after scanning a network, downloads the required software from the media such as a PC server, Smart card, or memory card, or over the air (OTA). The problem is the long downloading time and slow speed of data transfer [11]. In some recent works reported in [4, 12-14] the two dimensional s of the OFDM subcarriers are assigned to each network and each user of each networks. The system operated at the total transmission bandwidth and different CI codes that is transmitting antenna transmits at the same bandwidth with different s. The transmitted signal for the k th network (k=0, 1, 2-1) in the CI/OFDM based transmitting system is [5]: S k (t) = 1 1 a ki g Tk (t it )e j 2 (if )t e ji k. (2) i=0 where, f = 1/T b (T b is the bit rate), the sub-carrier frequency separation and k = (2 / )k is the phase offset used to generate for k network spreading code. Considering the entire -networks, the CI/OFDM transmitted signal is: 1 1 S(t) = 1 a ki g Tk (t it )e j 2 (i f )t e ji k (3) k=0 i=0 Design of Future SDR for All-IP Heterogeneous etwork Recent Patents on Signal Processing, 2010, Volume 2 15 The received signal is: 1 r(t) = 1 k=0 1 ki a ki g Tk (t it )e j 2 (i f )t e ji k e j ki + n(t) (4) i=0 where ki and ki are the fade parameter and phase offset introduced into the i th carrier of k network by the frequency selective Rayleigh fading channel, and n(t) is additive white Gaussian noise (AWG). After removing the sub-carrier frequency and phase offset i k, the decision vector r = (r 0, r 1, r 2,..., r 1 ) becomes: r kj = ki ki + kj kj + ji ji cos i( k j ) j=0,ji j=0,jk The second term is caused by: (a) Inter-carrier interference (ICI) which occurs due to Doppler frequency shift ( f D ) and, (b) Inter-symbol interference (ISI) that occurs due to multi-path propagation. In 4G heterogeneous network the user data is transmitted by using OFDM based multiplexing technique [9]. At the transmitting site, the serial binary information bits are transmitted to the receiver end using OFDM-based multiplexing technique. In the recent CI-based OFDM multiplexing technique [9, 10, 15, 16], all sub-carrier frequencies for each network share the same frequency band [4, 12]. The s such as, e j k, e j 2 k, e j 3 k, e j 4 k and e j 5 k differentiate the transmitting signals corresponding to each network. IX. SYSTEM MODEL OFDM technique can be written mathematically as [17]: M 1 1 S(t) = X ( p+q) (t)exp j2 f ( p+q) t, (6) p=0 q= (5) where, f is sub-carrier frequency and is the total number of sub-carrier and M is the number of users. In Fig. (4), the black arrow represents the OFDM sub-carrier to carry data and the red arrow represents the pilot carrier i.e. it indicates the start of the set of sub-carriers assigned to a particular user. For the OFDM sub-carrier in (6) and in Fig. (4a, b), all the sub-carriers have the same phase. In Fig. (4b), each symbol consists of a group of sub-carriers, where each subcarrier has a unique carrier frequency with the same phase. Each OFDM symbol in this figure has different sub-carrier frequency to maintain the orthogonality between the subcarrier of a symbol and that between the sub-carrier of other symbol. Each symbol is separated from other by a guard band to minimize the inter-symbol interference (ISI). Carrier interferometry OFDM CI/OFDM) is another multiplexing technique to minimize the effect of ISI and ICI. In CI/OFDM, a unique is assigned to each OFDM subcarrier. Mathematically the CI/OFDM symbol can be written as [6] 1 S(t) = X i (t)exp( j2 f i t)exp j k. (7) i=0 where, k = 2 k; k=0, 1, 2, 3 CI/OFDM is the same as OFDM, but only the difference is that a unique is assigned to each sub-carrier. The CI/OFDM sub-carriers are not only different in sub-carrier frequency but also different in phase offset as shown in Fig. (5). In Fig. (5), the total bandwidth (W) is subdivided to each of the OFDM symbol that is, W=W 1 +W 2 +W W n. Again the bandwidth of each OFDM symbol is divided into equal sub-carrier frequency and assigned to each sub-carrier. In Fig. (5b), the sub-carrier of CI/OFDM differs in frequency and phase i.e. different CI-code is assigned to each sub-carrier of individual OFDM symbol. Pilot carrier Data carrier OFDM Symbol OFDM Symbol OFDM Symbol Fig. (4a). OFDMA multiple access technique. phase symbol symbol symbol Fig. (4b). OFDM sub-carrier with different carrier frequency and same phase. Frequency 16 Recent Patents on Signal Processing, 2010, Volume 2 Alam and Sobhan Phase w 1 w 2 w 3 w n OFDM symbol OFDM symbol OFDM symbol OFDM symbol Frequency Fig. (5a). Each OFDM symbol is distributed in to sub-carriers. Phase w 1 w 2 w 3 w n OFDM symbol OFDM symbol OFDM symbol OFDM symbol Frequency Fig. (5b). Each sub-carrier experiences equal phase offset. A. Transmitter Design In Fig. (5b), the frequency band W 1 is assigned to the first OFDM symbol. We consider that the first OFDM symbol contains the sub-carriers represented by C 1, C 2, C 3 C i.e. the total number of sub-carriers is within the first OFDM symbol. ow, the sub-carrier frequencies are f 1,f 2,,f assigned to each sub-carrier, where W 1 = f 1,f 2,,f. The OFDM symbol can be represented as [6] S(t) = X i (t)exp j(2 f i t), (8) where X is the modulated mapping signal. In CI/ OFDM a CI-code is assigned to each sub-carrier, and the resultant CI/ OFDM symbol [6] S(t) = X i (t)exp j(2 f i t) exp j( 2 i). (9) The 4G Heterogeneous network accesses any network using a user terminal device. The OFDMA technology is used to access any kind of networks having different fre
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