Design Matched Filter for Digital Transmission Ethernet

Design Matched Filter for Digital Transmission Ethernet Eman Salem Electrical Engineering Department Benha Faculty of Engineering Benha University - Egypt Eman.salem@bhit.bu.edu.eg Hossam Labeb Electrical Engineering Department Benha Faculty of Engineering Benha University - Egypt @bhit.bu.edu.eg Abdelhalim Zekry Electronics and Communications Department Faculty of Engineering Ain Shams University - Egypt aaazekry@hotmail.com ABSTRACT Keywords Digital transmission makes out the major part of the digital communication networks. The core of the communication networks is based on digital carriers. Local area networks exchange their information on digital carriers called Ethernet. Unfortunately, the signal is contaminated by thermal noise. These noise signals can be partly removed by the matched filter. Ethernet is the most ubiquitous networking technology. It has grown from its roots in enterprise networks, and now addresses other markets such as data centers, storage, metro, wide area, and carrier networks. The IEEE 802.3 Ethernet Working Group develops Ethernet s physical layer standards and distinguishes each of these links by its port type or port name. In this paper, we show simulation results of matched filter in fast Ethernet system which supports 100Mbps data rate and 1 Gigabit Ethernet which supports 1000Mbps data rate. Ethernet, fast Ethernet, Gigabit Ethernet, matched filter, Simulation, BER. 1. INTRODUCTION Ethernet is the most common type of connection computers in a local area network (LAN). The original Ethernet was created in 1976 at Xerox s Palo Alto Research Center (PARC). It has gone through four generations (standard Ethernet (traditional), fast Ethernet, 1Gbps Ethernet and 10Gbps). Ethernet technologies are still in constant evolution since its inception in 1976, thus increasing the ability to expand and accommodate the Permanent largest possible number of devices that are connected with the possibility of securing transport at high speeds during small times. Fast Ethernet began to be widely deployed in the mid-1990s. Fast Ethernet supports a maximum data rate of 100 Mbps. It is named because original Ethernet technology supported only 10 Mbps. Ethernet networks use a variety of cable types (such as fiber optics and twisted pair cable). Gigabit Ethernet is the version of I

Ethernet. Gigabit Ethernet offers higher performance 1000Mbps (1Gpbs) that is one hundred times faster than the original Ethernet. 2. ETHERNET OVERVIEW Ethernet is the most widely deployed Local Area Network (LAN) protocol and has been extended to Metropolitan Area Networks (MAN) and Wide Area Networks (WAN). The major advantages that characterize Ethernet can be stated as its cost efficiency, bit rate increase (from 10 Mbps to 10 Gbps) and simplicity. ). It has gone through four generations (standard Ethernet (traditional), fast Ethernet, 1Gbps Ethernet and 10Gbps). Standard Ethernet The Standard Ethernet defines several physical layer implementations; four of the most common, are shown in Figure (1).[1] garden hose and too stiff to bend with your hands. 10Base5 was the first Ethernet specification to use a bus topology [1]. 10Base2: Thin Ethernet The second implementation is called 10Base2, thin Ethernet, or Cheaper net. 10Base2 also uses a bus topology, but the cable is much thinner and more flexible. The cable can be bent to pass very close to the stations [1]. 10Base-T: Twisted Pair Ethernet The third implementation is called 10Base-T or twisted pair Ethernet. 10Base-T uses a physical star topology. The stations are connected to a hub via two pairs of twisted cable [1]. 10Base-F: Fiber Ethernet Although there are several types of optical fiber 10Mbps Ethernet, the most common is called10base-f. 10Base-F uses a star topology to connect stations to a hub. The stations are connected to the hub using two fiber-optic cables [1]. Encoding and Decoding Figure 1:Categories of Standard Ethernet 10Base5: Thick Ethernet The first implementation is called 10Base5, thick Ethernet, or Thicknet. The nick name derives from the size of the cable, which is roughly the size of a All standard implementations use digital signaling (baseband) at 10Mbps.At the sender, data are converted to a digital signal using the Manchester scheme; at the receiver, the received signal is interpreted as Manchester and decoded into data. Figure (2) shows the encoding scheme for Standard Ethernet [1]. 2

Fast Ethernet implementation at the physical layer can be categorized as shown in Figure (3). Figure 2: Encoding in a Standard Ethernet implementation. Fast Ethernet Fast Ethernet supports a maximum data rate of 100 Mbps. It is so named because original Ethernet technology supported only 10 Mbps. Fast Ethernet began to be widely deployed in the mid-1990s as the need for greater LAN performance became critical to universities and businesses. IEEE created Fast Ethernet under the name 802.3u. Fast Ethernet is backward compatible with Standard Ethernet, but it can transmit data 10 times faster at a rate of 100Mbps.The goals of Fast Ethernet can be summarized as follows [1]: 1. Upgrade the data rate to 100Mbps. 2. Make it compatible with Standard Ethernet. 3. Keep the same 48-bit address. 4. Keep the same frame format. 5. Keep the same minimum and maximum frame lengths. The physical layer in Fast Ethernet is more complicated than the one in Standard Ethernet. We briefly discuss some features of this layer [1]. Figure 3: Fast Ethernet implementations. 100Base-TX Uses two pairs of twisted pair cable (either category5 UTP or STP). For this implementation, the MLT-3 scheme was selected since it has good bandwidth performance However, since MLT-3 is not a self-synchronous line coding scheme, 4B/5B block coding is used to provide bit synchronization by preventing the occurrence of a long sequence of 0s and 1s.This creates a data rate Of 125Mbps, which is fed into MLT-3 for encoding [1]. 100Base-FX Uses two pairs of fiber optic cables. Optical fiber can easily handle high Bandwidth requirements by using simple encoding schemes. NRZ-I scheme was selected for this implementation. However, NRZ-I has a bit synchronization problem for long sequences of 0s (or 1s, based on the encoding).to overcome this problem, the designers used 4B/5B block encoding as we described for 100Base- TX. The block encoding increases the bit 3

rate from 100 to 125Mbps, which can easily be handled by fiber optic cable [1]. Gigabit Ethernet Gigabit Ethernet is the version of Ethernet. It offers 1000Mbps (1 Gbps) bandwidth, that is 100 times faster than the original Ethernet, yet is compatible with existing Ethernets [2]. Gigabit Ethernet can be categorized as either a two wire or a four wire implementation as shown in figure (5). Table 1: Summary of Fast Ethernet implementations Encoding Manchester encoding needs a 200-Mbaud bandwidth for a data rate of 100Mbps, which makes it unsuitable for a medium such as twisted-pair cable. For this reason, the Fast Ethernet designers sought some alternative encoding/decoding scheme. However, it was found that one scheme would not perform equally well for all three implementations. Figure 5: Gigabit Ethernet implementations. Therefore, three different encoding schemes were chosen (see Figure 4) [1]. Table 2: Summary of Gigabit Ethernet implementations. Encoding Figure (6) shows the encoding/decoding schemes for the four implementations. Figure 4: Encoding for Fast Ethernet implementation. 4

Figure 6: Encoding in Gigabit Ethernet implementations. Ten Gigabit Ethernet As advances in hardware continue to provide faster transmissions across networks, Ethernet implementations have improved in order to capitalize on the faster speeds. Fast Ethernet increased the speed of traditional Ethernet from 10 megabits per second (Mbps) to 100 Mbps. This was further augmented to 1000 Mbps in June of 1998, when the IEEE defined the standard for Gigabit Ethernet (IEEE 802.3z). Finally, in 2005, IEEE created the 802.3ae standard introduced 10 Gigabit Ethernet, also referred to as 10GbE. 10GbE provides transmission speeds of 10 gigabits per second (Gbps), or 10000 Mbps, 10 times the speed of Gigabit Ethernet [3]. Physical Layer The physical layer in Ten Gigabit Ethernet is designed for using fiber optic cable over long distances. Three implementations are the most common: 10GBase-S, 10GBase-L, and 10GBase-E. Table (3) shows a summary of the Ten- Gigabit Ethernet implementations [1]. Table 3: Summary of Ten-Gigabit Ethernet implementations. 3. Fast Ethernet design Figure (7) illustrates the main building blocks of fast Ethernet systems (100basefx) Figure 7: Block Diagram of fast Ethernet system. The main component is block coding (4B/5B) which converts each 4-bit of information into a 5-bit code resulting in an effective bit rate of 125 Mbps according to the table (4) which shows the corresponding pairs used in 4B/5B encoding. Table 4: 4B/5B mapping codes [4]. 5

Then, we used scrambler to the purpose of scrambling is to reduce the length of strings of 0s or 1s in a transmitted signal, since a long string of 0s or 1s may cause transmission synchronization problems. the basic system of scrambler transmitter is shown in figure (8). signal has a transition at a clock boundary if the bit being transmitted is a logical 1, and does not have a transition if the bit being transmitted is a logical 0 figure (10) shows example of NRZI coding. Figure 8: The basic system of the scrambler transmitter [5]. A circuit in Figure (9) show scrambler which we used in design 100base-fx Its characteristic polynomial is 1+ x 9 + x 11 because the taps are connected at the output of registers 9 and 11, which repeats its sequence after 2 N = 2047 bits [6]. Figure 9: scrambler with polynomial 1 + x 9 + x 11 [6] The (scrambled) bit-stream is encoded with a NRZI encoding. NRZI is a method of mapping a binary signal to a physical signal for transmission over some transmission media. The two level NRZI Figure 10: Example NRZI encoding [7]. Before a signal is transmitted over a channel, the bits of information are coded into symbols using quadrature Amplitude Modulation (QAM). For this modulation scheme, a symbol is encoded into discrete signal levels. The amplitude of each pulse is proportional to the amplitude of the message signal at the time of sampling. The Raised Cosine Transmit Filter up samples and pulse shaping of the input signal using a square root raised cosine FIR filter, Figure (11) shows Impulse response of pulse shaping filter RRC at Group delay = 10, N samples = 5 and roll off factor = 0.001 which we used in our design. Figure 11: impulse response of RRC 6

The AWGN Channel adds white Gaussian noise to transmitted signal. We used AWGN channel with SNR= 12dB. The signal has now been transmitted over the channel and it needs to be recovered. The steps to recover the original signal are as follows: 1. Recover the signal from the RRC (root raised cosine filter). 2. Demodulate the signal. 3. Decoding 4. Matlab model Figure (12) illustrates the constructed Simulink model. 5. Simulation results The simulation results at each step are shown below. The results are displayed in the form of snapshots of scope signals. Signals at Transmitter By using Bernoulli Binary Generator block, we generated binary data stream of 100Mbps data rate. The serial data stream is converted into 4-bit parallel. Each 4-bit of information are converted into a 5-bit code resulting in an effective bit rate of 125 Mbps over the transmission media by 4B5B encoder shown in the figure (13) Figure 13: 5 bit after 4b/5b encoder. Then, we used scrambler to reduce the length of strings of 0s or 1s in a transmitted signal, since a long string of 0s or1s may cause transmission synchronization problem.the signal after scrambler is shown in figure (14). Figure 14: Scrambled signal. Figure 12: Matlab model for fast Ethernet (100basefx). The (scrambled) bit-stream is encoded with a NRZI encoding to convert digital data to digital signal to be suitable for 7

transmission over some transmission media as shown in figure (15). Figure 18: Signal after AWGN. Figure 15: Signal after NRZI. Before a signal is transmitted over a channel, the bits of information are coded into symbols using (QAM) modulation figure (16) illustrates the signal after QAM modulation. Signal at Receiver The first step is to recover the signal from the RRC. Figure (19) illustrates signal after matched filter. Figure 19: signal after matched filter Figure 16: Modulated Signal. Then, we used square root raised cosine filter (pulse shaping filter) the signal after pulse shaping filter is shown in figure (17). After filtering the signal with the RRC, we'll demodulate the signal using QAM as shown in figure (20). Figure 20: demodulated Signal Figure 17: Signal after pulse shaping filter. Then, we used NRZI decoder to convert digital signal to binary signal as shown in figure (21). Then, adds white Gaussian noise to signal as shown in figure (18). Figure 21: Digital data after line decoding. 8

Then, descrambles input signal we used the same scrambler polynomial figure (22) show signal after descrambler. Figure 24: signal after scrambler and before descrambler Figure 22: Signal after descrambler. After descrambler we recover 5 bits which enter to 5b4b decoder to obtain 4 bits which was transmitted the figure (23) shows Signal after 4B5B encoder (delayed by 10 samples) and after descrambler. Finally we obtain the recovered signal, figure (25) shows transmitted signal (delayed by 4 samples) and received signal. Figure 23: signal after 4B/5B encoder and descrambler Figure (24) shows Signal after scrambler (delayed by 40 samples) and signal before descrambler. Figure 25: Signals Transmitted and Received 9

6. BER performance The BER plot showed the different responses of the model corresponding to the different values of SNR..The BER is supposed to be decreasing with the increase in SNR. To investigate the modified model performance, we compared its BER to the theoretical one. Figure (26) shows theoretical QAM. Figure (27) shows BER comparison between theoretical QAM and simulation results of model at different values of rolloff factors R of square root raised cosine filters. Figure 27: BER comparison between theoretical QAM and simulation results of model at different values of R. Figure 26: BER of theoretical QAM. Figure (28) shows BER comparison between theoretical QAM and simulation results of model at R=0.01 and R =0.001. Figure 28: shows BER comparison between theoretical QAM and simulation results of model at R=0.01 and R =0.001. 10

7. Gigabit Ethernet design Figure (29) illustrates the main building blocks of 1Gigabit Ethernet system over fiber optic. Figure 29: Block Diagram of 1Gigabit Ethernet system. The main component is block coding (8B/10B) which converts each 8-bit of information into a 10-bit code resulting in an effective bit rate of 1.25 Gbps. The 8B/l0B block coding is actually a combination of 5B/6B and 3B/4B encoding, as shown in Figure (30). Figure 30: 8B/l0B block encoding [8]. Figure 31: Matlab model for Gigabit Ethernet over fiber optic. 8B/10B Encoder The serial data stream is converted into 8- bit parallel. Each 8-bit of information are converted into a 10-bit code resulting in an effective bit rate of 1.25 Gbps over the transmission media by 8B/10B encoder. This coding scheme is used for high-speed serial data transmission. So, we design 5B\6B encoder, 3B\4B encoder and disparity which keep track of excess 0s over 1s (or 1s over 0s). 8. Matlab model Figure (31) illustrates the constructed Simulink model of Gigabit Ethernet. Figure 32:8B/10B coding scheme. The coding scheme breaks the original 8- bit data into two blocks, 3 least significant bits (y) and 5 most significant bits (x). 11

From the least significant bit to the most significant bit, they are named as H, G, F and E, D, C, B, A. The 3-bit block is encoded into 4 bits named j, h, g, f. The 5- bit block is encoded into 6 bits named i, e, d, c, b, a. As see in Figure (32), the 4-bit and 6-bit blocks are then combined into a 10-bit encoded value [9]. We design 5b/6b encoder and 3b/4b encoder by logic gates according to table (5) and table (6). Table 5: 4b/5b code. Disparity A DC-balanced serial data stream means that it has the same number of 0 s and 1 s for a given length of data stream. In order to create a DC-balanced data stream, the concept of disparity is employed to balance the number of 0 s and 1 s. The disparity of a block is calculated by the number of 1 s minus the number of 0 s. The value of a block that has a zero disparity is called disparity neutral. Running Disparity The transmitter assumes a negative Running Disparity (RD-) at start up. When an 8-bit data is encoding, the encoder will use the RD- column for encoding. If the 10-bit data been encoded is disparity neutral, the Running Disparity will not be changed and the RD- column will still be used. Otherwise, the Running Disparity will be changed and the RD+ column will be used instead. Similarly, if the current Running Disparity is positive (RD+) and a disparity neutral 10-bit data is encoded, the Running Disparity will still be RD+. Otherwise, it will be changed from RD+ back to RD- and the RD- column will be used again. The state diagram in Figure (33) describes how the current Running Disparity is calculated [9]. Table 6: 3b/4b code Figure 33:Running disparity state machine. 12

Disparity design in transmitter We use MATLAB-SIMULINK toolboxes to simulate disparity as shown in figure (34). Non Return to Zero Invert (NRZI) Encoder We design NRZI encoder by matlab as shown in figure (36), we used XOR gate and D flip flop. Figure 34: Disparity design at transmitter. Scrambler Figure 36: Non Return To Zero Invert (NRZI) Encoder. Raised Cosine Transmit Filter Figure 35: The basic system of the scrambler transmitter. The purpose of scrambling is to reduce the length of strings of 0s or 1s in a transmitted signal, since a long string of 0s or1s may cause transmission synchronization problems the basic system of scrambler in transmitter is shown in figure (35). We used scrambler 16 bits with characteristic polynomial is 1+ x 11 + x 13 + x 14 + x 16. Scramble polynomial :A polynomial that defines the connections in the scrambler [1 0 0 0 0 0 0 0 0 0 0 1 0 1 1 0 1]. The Raised Cosine Transmit Filter upsamples and pulse shaping of the input signal using a square root raised cosine FIR filter. Figure (37) shows Impulse response of pulse shaping filter RRC at Group delay = 25, N samples = 10 and roll off factor = 0.0025 which we used in our design Figure 37 : impulse response of RRC. The AWGN Channel adds white Gaussian noise to transmitted signal. We used AWGN channel with SNR= 12dB. 13

The signal has now been transmitted over the channel and it needs to be recovered. The steps to recover the original signal are as follows: 1. Recover the signal from the RRC (root raised cosine filter). 2. Demodulate the signal. 3. Decoding 9. Simulation results Signals at Transmitter By using Bernoulli Binary Generator block, we generated binary data stream of 1Gbps data rate. The serial data stream is converted into 8-bit parallel. Each 8-bit of information are converted into a 10-bit code resulting in an effective bit rate of 1.25 Gbps over the transmission media by 8B/10B encoder shown in the figure (38). The (scrambled) bit-stream is encoded with a NRZI encoding to convert digital data to digital signal to be suitable for transmission over some transmission media as shown in figure (40). Figure 40: Signal after line coding Before a signal is transmitted over a channel, the bits of information are coded into symbols using (QAM) modulation figure (41) illustrates the signal after QAM modulation. Figure 41: Modulated Signal Figure 38: 5 bit after 8b/10b encoder. Then, we used scrambler 16 bits to reduce the length of strings of 0s or 1s in a transmitted signal, since a long string of 0s or1s may cause transmission synchronization problem. The signal after scrambler is shown in figure (39). Then, we used square root raised cosine filter (pulse shaping filter) the signal after pulse shaping filter is shown in figure (42). Figure 42: Signal after pulse shaping filter. Figure 39: Scrambled signal. 14

Then, adds white Gaussian noise to signal as shown in figure (43). Then, descrambles input signal we used the same scrambler polynomial figure (47) show signal after descrambler. Figure 43: Signal after AWGN. Signal at Receiver The first step is to recover the signal from the RRC. Figure (44) illustrates signal after matched filter. Figure 47: Signal after descrambler before 10b/8b decoder we recover 10 bits which enter to 10b/8b decoder to obtain 8 bits which was transmitted the figure (48) shows Signal after 8B/10B encoder (delayed by 20 samples) and before 10b/8b decoder. Figure 44: Signal after matched filter. After filtering the signal with the RRC, we'll demodulate the signal using QAM as shown in figure (45). Figure 45:Signal after demodulation Figure 48: signal after 8B/10B encoder and before decoder. Then, we used NRZI decoder to convert digital signal to binary signal as shown in figure (46). Figure 46: Digital data after line decoding. 15

Finally we obtain the recovered signal. Figure (49) shows transmitted signal (delayed by 8 samples) and received signal. Figure (51) shows BER comparison between theoretical QAM and simulation results of model at different values of rolloff factors R of square root raised cosine filters. Figure 49: Transmitted and Received Signals 10. BER performance The BER plot showed the different responses of the model corresponding to the different values of SNR..The BER is supposed to be decreasing with the increase in SNR. To investigate the modified model performance, we compared its BER to the theoretical one. This is done using bertool. BERTool is a bit error rate analysis application for analyzing communication systems bit error rate (BER) performance. Figure (50) shows theoretical QAM. Figure 51: BER comparison between theoretical QAM and simulation results of model at different values of R. Figure (52) shows BER comparison between theoretical QAM and simulation results of model at R=0.025 and R =0.0025. Figure 50: BER of theoretical QAM.. Figure 52: shows BER comparison between theoretical QAM and simulation results of model at R=0.025 and R =0.0025. 16

The BER results indicate that the system response changes with the change of the values of roll off factor R of square root raised cosine filters. The BER performance at R=0.0025 is better than the BER performance at R=0.025. 11. CONCLUSION Ethernet is the most widely used local area network (LAN) technology. The original version of Ethernet supports a data transmission rate of 10 Mb/s. Newer versions of Ethernet called "Fast Ethernet" and "Gigabit Ethernet" support data rates of 100 Mb/s,1 Gb/s and 10Gbps. An Ethernet LAN may use coaxial cable or fiber optic cable. "Bus" and "Star" wiring configurations are supported. There are three types of Fast Ethernet: 100BASE-TX for use with UTP cable, 100BASE-FX for use with fiber-optic cable, and 100BASE-T4 for use with UTP cable. We design fast Ethernet (100base Fx). We designed 100BaseFX which use fiber optic cable. Gigabit Ethernet is the version of Ethernet. It offers 1000Mbps (1 Gbps ) bandwidth, that is 100 times faster than the original Ethernet. At 100 Mbps, a technique known as 4B/ 5B is used to provide extra symbols for encoding.different techniques for line encoding are used depending whether copper or fiber is used as the physical layer. The line encoding varies depending on the physical layer used. In our design we used NRZI line coding which use in fiber optic. In design 1 Gigabit Ethernet over fiber optic system we used 8B/10B technique which converts 8 bits to 10 bits. And line coding NRZI which is suitable for fiber optic. we developed a MATLAB model of matched filter for fast ethernet (100baseFx) which support 100 Mbps and 1 Gigabit ethernet over fiber optic. Finally, a complete systems was designed and tested. 12. REFERENCES [1] B. A. Forouzan, Data Communications and Networking, McGraw-Hill Companies, Inc, ISBN-13 978-0-07-296775-3 - ISBN-to 0-07- 296775-7, Fourth Edition, 2007. [2] V. Moorthy, Gigabit Ethernet, Aug 14, 1997. [3] L. Parziale, D.T. Britt, C.Davis, J. Forrester and W. Liu, TCP/IP Tutorial and Technical Overview, International Business Machines Corporation IBM Corp, Eighth Edition, 2006 [4] N. Vlajic, Digital Transmission of Digital Data: Line and Block Coding, Digital Transmission Modes, York University, Computer Science, CSE 321, 2010. [5] M. P. Spratt, The Use of Scramblers with an Anti-Locking Circuit, Hewlett- Packard Laboratories, December 1992. 17

[6] V. A. Pedroni, Digital Electronics and Design with VHDL, Morgan Kaufmann, 2008. [7] C. Yao, Line Coding in Digital Communication, Fiber Optic Training & Tutorials FAQ, Tips & News, November 2011. [8] A. Balchunas, Ethernet Technologies, v2.01, 2012. [9] 8b/10b Encoder/Decoder, Lattice Semiconductor Corp, February 2012. 18