Error Performance of Burst-Mode Receivers - IEEE Xplore

Error Performance of Burst-Mode Receivers Volume 2, Number 3, June 2010 Surinder Singh Neeraj Sharma

DOI: 10.1109/JPHOT.2010.2047636 1943-0655/$26.00 ©2010 IEEE

IEEE Photonics Journal

Error Performance of Burst-Mode Receivers

Error Performance of Burst-Mode Receivers Surinder Singh 1 and Neeraj Sharma 2 1 2

Department of Electronics and Communication Engineering, Sant Longowal Institute of Engineering and Technology, Longowal 148106, Sangrur, Punjab, India Department of ECE, SSG Punjab University Regional Centre, Hoshiarpur 146020, India DOI: 10.1109/JPHOT.2010.2047636 1943-0655/$26.00 Ó2010 IEEE

Manuscript received March 3, 2010; revised March 29, 2010 and March 30, 2010. First published Online April 5, 2010. Current version published May 28, 2010. Corresponding author: S. Singh (e-mail: [email protected]).

Abstract: This paper reports a mathematical model for the evaluation of the bit error rate (BER) performance of burst-mode receivers by taking the effect of random noise and charging/ discharging parameters of the receiver into consideration. The distribution of the threshold voltages will be similar to that of the distribution of the values corresponding to logical 1’s of the preamble for threshold setting. The threshold setting will also vary when a long string of consecutive 0’s arrive in the incoming data that report errors in detection. The average threshold is determined for a particular bit position in the consecutive string of 0’s. The expression based on the threshold is also used to determine the BER of the receiver. Index Terms: BER, burst-mode receiver, OLT, ONT.

1. Introduction Future-generation optical networks require fast packet switching to support multimedia applications, and a very high transmission speed is required. As the bit rate increases beyond the capacity of electronic processing, it is desirable to reduce the amount of electronic processing at each node. Recent advances in erbium-doped fiber amplifiers, high-speed time-division multiplexing/ demultiplexing, high-density wavelength-division multiplexing (WDM) devices and optical tunable filters, etc., provides an impetus to develop a future all-optical network that is capable of supporting multiple access and multimedia services at a very high bit rate. In the last several years, improved wavelength-division multiplexed (WDM) technology has increased the total throughput of link systems, but that of node systems is still restricted by limitations of electrical switch capacity [1]. In networks of this type, the wavelength dependence of the optical devices and the pathdependent power loss generate power fluctuations from one packet to the next, and the path length differences between each packet generate packet arriving timing jitter. The optimum threshold level and decision timing differ from packet to packet at the optical burst-mode packet receiver. The conventional receivers are unsuitable for this kind of applications because they cannot instantaneously handle the different arriving packets with large difference in optical power and phase alignment. It is therefore necessary to design receivers, which can adapt on a packet-bypacket basis. These types of receivers are called burst-mode receivers.

2. Background Ota and Swartz did the pioneering work to develop burst-mode receiver for high-speed optical data transmission systems [2], [3]. The most important requirement of burst-mode receivers is to set a threshold level according to the power level of the incoming data packet to be detected. By using a few preamble bits in the data stream to determine the detection threshold for the subsequent burst,

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a dc-coupled burst-mode optical receiver with an automatic threshold control circuit was realized [3]. The receiver sensitivity was 37.5 dBm with a bit error rate ðBERÞ G 109 at a bit rate of 900 Mb/s and a dynamic range of 23 dB. Then, a high-speed PIN HBT monolithic photoreceiver was demonstrated for both continuous and burst-mode data [4]. The measured sensitivities were 21. 5 dBm and 18.6 dBm at 2.5 Gb/s and 5 Gb/s, respectively, under continuous-mode operation. There are mainly two effects that degrade the BER performance of burst-mode receivers as compared with conventional receivers: the random Gaussian noise, which is always present at the receiver, and the finite charging/discharging time decays of capacitance of the threshold detection circuitry, which yields a different threshold level when a long string of consecutive 0’s appear in the data. Corresponding to these factors, some work has already taken place. Eldering [5] evaluated the BER penalty due to Gaussian noise during the determination of threshold setting from the preamble field. Only 1’s were used in the preamble and the threshold estimated from these 1’s was assumed to be effected by random Gaussian noise. This study ignored the fact that the threshold setting will change when a long string of 0’s appear in the data pattern. It assumed the discharging parameter ðK Þ to be equal to zero. This value of parameter K corresponds to an infinite discharging RC-time constant of the peak detector. Based on these assumptions, the power (sensitivity) penalty with respect to conventional receivers was 3.00 dB when a single bit was used to establish the threshold. This penalty decreased to 0.94 dB when 4 bits were used, 0.51 dB when 8 bits were used, and 0.28 dB when 16 bits were used. With 36 bits in the preamble for amplitude recovery, the penalty was less than 0.2 dB. Another model studied the affect of finite charging/discharging time decays of capacitance of the adaptive threshold detection circuitry. It assumed that no preamble is used and threshold is set adaptively in each bit interval, which varies according to the data pattern [6]. It studied the effect of finite charging/discharging parameters of the peak detector and ignored the effect of noise-induced penalty on threshold determination. The model explained the error performance of the receiver for both uncoded random data and 4B5B/5B6B line coded data. It was concluded that the BER performance of the receiver is better for coded data than uncoded data. Further, a short pseudorandom length of uncoded NRZ signal had better error performance than a longer one. Valdes [7] provided a very simple analytical expression for the noise-induced penalty of burst-mode receivers which depended only on the number of bits used in the preamble. It analyzed the affect of scaling factor, which relates the acquired signal amplitude with the proper threshold amplitude, on the error performance of the receiver, when both 1’s and 0’s are used in the preamble. This parameter was ignored in the earlier work. This model is also applicable for the evaluation of the receiver’s performance where the threshold is determined entirely from the preamble field. In burst-mode operation, there are occasions when no data is present. Hence, a minimum dc-offset voltage is generally applied to the decision threshold to avoid noise-induced errors when no input is present, but this offset reduces sensitivity of the receiver. In a study, it has been concluded that if dynamic offset is used in burst-mode receiver, then the penalty caused due to fixed offset can be reduced. This result has been derived both theoretically and experimentally [8]. A good solution was proposed to avoid the power penalty due to finite extinction ratio by using a Bdark-level compensator[ subcircuit in the receiver [9]. This circuitry can automatically measure and subtract out the signal due to the background light in the network. The error performance of an optical receiver using an optical preamplifier and an optical filter was studied [10]. The study included the effects of pulse distortion, intersymbol interference (ISI) resulting from filter characteristics, and the noise characteristics. The optical power penalty was 1.38 dB and 0.19 dB for 10 bits of preamble, respectively. A high sensitivity (29 dBm) peak detector circuit has been designed for 1.25-Gb/s data rate, which avoids sensitivity penalty due to nonzero extinction ratio [11]. An integrated 155-Mb/s burst-mode receiver for passive optical network (PON) applications was presented [12]. The chip had a wide dynamic range (22 dB) and temperature range (40 C to þ85 C). The chip was implemented using a 0.8-m 35-GHz SiGe BiCMOS technology and occupies an area of 4:3 4:9 mm2 with a power consumption of 500 mW from a supply voltage of

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5 V. Recently, a 10-Gb/s burst-mode optical receiver for receiving asynchronous bursts with power variations of 7 dB was presented in [13]. It was shown that the addition of an electronically controlled semiconductor optical amplifier for optical power equalization before the receiver extends the burstto-burst dynamic range from 7 dB to 16.5 dB. Some companies manufacture burst-mode receivers commercially, namely, Optical Zonu Ltd. and OKI Ltd. Optical Zonu, has recently developed a single-fiber transceiver which comprises a burst-/continuous-mode receiver (1.25 Gb/s) and a continuous-mode transmitter for operation in Ethernet passive optic networks [14]. Average receiver sensitivity is 25 dBm. The transmitter incorporates an Automatic Laser Power Control circuit (APC) to maintain the optical power and extinction ratio over a case temperature of 20 C to þ70 C. OKI Ltd. (a Japan-based company) also deployed a transceiver working at 155 Mb/s for burst-mode reception and 622 Mb/s for continuous-mode transmission [15].

3. Classification of Burst-Mode Optical Receivers Burst-mode receivers can be classified according to their structures as well as according to how the threshold is set. Feedback type: In this configuration, a differential input/output transimpedance amplifier with a peak detection circuit is used determined by the peak detector circuit. The output of the preamplifier is coupled to a differential post amplifier for further amplification. In this method, it is the signal that forms a feedback loop. The instantaneous for the incoming signal is amplitude is recovered in the preamplifier [2]–[4], [9] and postamplifier is for voltage amplification of the detected signal. Feedforward type: In this type of receiver, the received signal is first amplified by a preamplifier and then divided into two parts. The first part of the output is coupled to a differential amplifier. The second part is fed to a peak detection circuitry to determine the amplitude of the received data [5], [11]. The operation for feedback type receivers is more stable than feedforward type, since a feedback loop ensures stability of the receiver, but a differential input/output preamplifier is needed. In feedforward receiver, a conventional preamplifier can be used in the receiver. Moreover, feedforward receivers have faster response to the burst data than the feedback type. However, the circuit needs to be carefully designed to prevent oscillations in the receiver. Burst-mode receivers can also be also be classified according to the way the threshold is set. The first type is that the receiver threshold is determined completely from the preamble field and held constant in the data field [5]. The second type is that the receiver threshold is adaptively determined according to the input signal [2]–[4], [6].

4. Burst-Mode Receiver in High-Speed All-Optical Multiaccess Networks All-optical multiaccess network is a very active area of research. The burst-mode receiver is especially suitable for various all-optical multiaccess networks based on packet transmission. For multiaccess network, a well-known example is the PON using TDMA technology. The PONs are a class of Bfiber-to-the-home[ or Bfiber-to-the-curb[ access networks that telephone and cable TV companies are starting to deploy to deliver voice, video programming, and high-speed Internet access to homes and businesses. In these networks (see Fig. 1), an optical line terminal (OLT) is installed at service provider facilities in the central office (CO), such as telephone company switching centers or cable TV head-ends, and optical network terminals (ONTs) are installed in homes, apartment and office buildings, or in neighborhood distribution hubs (in fiber-to-the-curb configurations). Communications signals travel between the OLT and ONT over optical fiber, with signals being routed from one OLT to as many as 32 ONTs. The term Bpassive[ refers to the fact that there are no electrically powered components along the network pathVonly the endpoints (the OLT and ONTs) are powered. As a result, service providers consider PONs to be an economical and reliable solution for bringing digital video programming and high-speed Internet access over into homes and offices. For these networks, the CO continuously sends its data to all the nodes via the passive optical splitters. Therefore, for the downlink, a conventional transmitter (at the CO) and a conventional

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Fig. 1. Passive optical network.

receiver (at each node) can be used. However, for the uplink, packet collisions have to be avoided. The network thus allows only one node to transmit its packet to the CO at one time. Packets following each other to the receiver at the CO are separated by a certain gap time. It is clear that in an all-optical TDMA network, a burst-mode receiver should be used in the CO [17], [18]. High sensitivity, wide dynamic range and fast response are important figures of merit for a burst-mode receiver. A 3-dB improvement on the sensitivity can increase the splitting ratio by a factor of 2, which almost doubles the number of subscribers that can be connected to the shared medium with little extra cost. A large dynamic range guarantees a long logical reach and increases the network flexibility. The receiver can effectively receive and handle bursty packets from various nodes with large geographical separation without severe synchronization requirement. In conclusion, burst-mode receivers are suitable for all these various types of all-optical multiaccess packet networks. In this paper, a mathematical model has been proposed to analyze the error performance and then determine the SNR penalty of burst-mode receivers taking into consideration random Gaussian noise and the finite charging/discharging parameters of the receiver.

5. Model and Assumptions The assumptions which have been made for the development of mathematical model of burst-mode receiver are as follows: 1) Only 1’s are used in the preamble of data packet, and each data packet contains L number of 1’s in the preamble which are used for establishing the threshold to determine the 1’s and 0’s in the subsequent data stream. 2) The received signal is corrupted by additive white Gaussian noise (AWGN). Hence, instantaneous threshold determined by the adaptive threshold detection circuit (represented by the random variable) has a Gaussian distribution. 3) Voltage level corresponding to logic 0 in the incoming data is 0 V. Hence, extinction ratio ðVoff =Von Þ is zero. 4) The probability of detecting a 0 as 1 ½Pð1=0Þ in the incoming data is far greater than the probability of detecting a 1 as 0 ½Pð0=1Þ in the incoming data, i.e., Pð1=0Þ Pð0=1Þ. Hence, Pð0=1Þ 0. 5) Analysis is independent of the bit rate and the pulse shape, i.e., there is no ISI. The first four assumptions represent that the models have the condition of threshold preamble, received corrupted signal, probability of 0 or 1, and voltage level for 0, but the last assumption shows that the system is free from any kind of interference or distortion. This is done to reduce the complexity of the model. However, in the experiment, the presence of interference certainly reduces the performance of the receiver.

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Fig. 2. Threshold variation of a burst-mode receiver.

The BER of a burst-mode receiver as follows: Pe ¼ Pð0ÞPe0 þ Pð1ÞPe1

(1)

where Pð0Þ and Pð1Þ are the probability of logic 0 and 1, respectively, appearing in the data pattern. Pe0 is the probability of detecting 1 when a 0 is transmitted, and Pe1 is the probability of detecting 0 when a 1 is transmitted. The received signal is corrupted by AWGN and the instantaneous threshold determined by the adaptive threshold detection circuit (represented by the random variable R) will have a Gaussian distribution. The probability density function for noise-corrupted threshold is given as [4] rffiffiffiffiffiffiffiffiffiffiffi h i N N 2 2 f ðRÞ ¼ =2 : exp N R V th 22

(2)

Here, VthN is the mean value of the threshold determined from the preamble bits, and is the rms noise averaged over one-bit bits for the detection of the threshold. By properly choosing the rising time constant of the peak detector, it is possible to make the charging time correspond to the N bits of the preamble. Due to finite charging and discharging time decays of the capacitor of the peak detector, the set threshold fluctuates during the data field (shown in Fig. 2). For these burst-mode receivers using adaptive threshold determination, the detected threshold in the data field can be represented by [16] Vth ½n; t ¼

Vth ½n 1; T expðt=f Þ Vth ½n 1; T þ ðVc Vth ½n 1; T Þ½1 expðt =r Þ

aðnÞ ¼ 0 aðnÞ ¼ 1

(3)

where Vth ½n; t is the threshold at time t in the bit interval, and 0 t T . T is the bit interval, and aðnÞ is the data symbol (B0[ or B1[) for the nth bit. Vc is the ideal threshold if the signal is received by a conventional receiver, and Br [ and Bf [ are the rising and holding time constants for the peak detection circuitry. The rising parameter and decay parameter for the peak detection circuitry are defined as

Kr ¼

T r

and K ¼

T : f

(4)

If the data bit is 0, the instantaneous threshold of the bit under consideration depends on the number of consecutive 0’s in the input data preceding the bit. After N bits of consecutive 1’s, the threshold will be VthN ¼ Vc ð1 e NKr Þ:

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Error Performance of Burst-Mode Receivers TABLE 1

Distributions of Consecutive 0’s in 4B5B/5B6B Line Coded Data

VthN will only approach ideal threshold Vc when NKr is large. Hence, a steady-state error can be defined as (6) e ¼ Vc VthN =Vc : A steady-state error e of 2% has been assumed. For e ¼ 0:02; Kr N ¼ 3:92. This relation between Kr and N has been used in the solution of the model. The average BER for uncoded NRZ data can be expressed as [5], [9] Pe ¼ Pð1ÞPe1 þ Pð0ÞPe0 ¼ Pð1ÞPe1 þ

Zþ1 n i X 1 1X f ðRÞ Pe0j dR 2iþ1 i j¼1 i¼1 1

n i X 1 1X ¼ Pð1ÞPe1 þ BERj ð0Þ 2iþ1 i j¼1 i¼1

(7)

where Pe0j ¼

Z1 j

h i 1 pffiffiffiffiffiffi exp ðV Voff Þ2 =22 dV 2

V th0

exp Q 2 ½j=2 pffiffiffiffiffiffi : ¼ 2Q½j

(8)

Q½j is the Q-factor of the jth bit in a consecutive string of zeroes in the incoming data. From [17] " ( Zþ1 pffiffiffiffi N N Qc 1 1ð1ÞeKr exp BERj ð0Þ ¼ Pp 2 2 p¼1 n X

1

e ðj1ÞK ejK K

)

!2 # y

2

exp ðQ2cy Þ dR: (9) Qc y

Here, y ¼ ððVc RÞ=Þ and ¼ epK are dependent on the input data. Pp is the probability for p consecutive 0’s in the incoming data. For a typical 4B5B or 5B6B data, statistical distributions for consecutive 0’s are obtained by simulation, and results are shown in Table 1 [6]. Therefore, BER for encoded data will be Pe ¼ Pð1ÞPe1 þ Pð0ÞPe0 ¼ Pð1ÞPe1 þ P1 BER 1 ð0Þ þ P2

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2 3 1X 1X BER j ð0Þ þ P3 BER j ð0Þ: 2 j¼1 3 j¼1

(10)

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Fig. 3. (a) BER versus K for uncoded NRZ data for different lengths of preamble N. (b) BER versus K for 4B5B/5B6B encoded data for different lengths of preamble N.

Fig. 4. (a) SNR penalty versus decay parameter K for uncoded NRZ data for different values of N. (b) Power penalty versus parameter K for 4B5B/5B6B encoded data for different values preamble bits.

6. Bit Error Analysis of Burst-Mode Receiver The graphs (see Fig. 3(a) and (b)) has been plotted between BER and decay parameter K corresponding to N ¼ 1, 2, 3, and 4 for uncoded NRZ data and 4B5B/5B6B line coded data. These values of N have been chosen such that they correspond to Kr equal to 3.91, 1.96, 1.30 and 0.98, respectively. The results show that a large K degrades the error performance seriously. This effect is more significant for uncoded data. The power penalty is plotted against the decay parameter K at BER of 109 for uncoded NRZ and 4B5B/5B6B encoded data in Fig. 4(a) and (b), respectively. The random length of uncoded data is assumed to be N ¼ 29 1. It is clear from Fig. 5(a) and (b) that the performance of receiver depends on decaying parameter as well as length of preamble field for large values of K . It is due to the reason that when discharging parameter is large, the receiver performance is controlled by the decay process of the instantaneous threshold. The power penalty versus Kr or length of preamble field shown in Fig. 5(a) and (b) for both types of data. From these results, it is clear that a larger preamble field will yield a better threshold setting in the preamble field, but at the same time, a large value of decaying parameter will degrade the receiver performance.

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Fig. 5. (a) Power penalty versus length of preamble for uncoded NRZ data for different values of parameter K . (b) Power penalty versus N for 4B5B/5B6B encoded data for different values of parameter K .

7. Conclusion and Future Scope It is concluded that large value of discharge parameter degrades the BER performance drastically. This effect is more pronounced for uncoded data. A longer preamble does not provide any significant BER improvement over four or five preamble bits. For both uncoded as well as encoded data, the BER penalty is independent of the length of the preamble field when the discharging time of the capacitor is not large. The value of the decay parameter over which the penalty becomes independent of the length of the preamble is smaller for uncoded data than that for the encoded data. This is due to much smaller length of the consecutive 0’s in encoded data. By decreasing the decay parameter, the power penalty can be reduced, but a large gap time between data packets would be required to completely discharge the capacitor so that its residual potential does not upset the threshold setting of the following packet. Hence, transmission penalty will be introduced. Therefore, there is a tradeoff between the penalty and network transmission efficiency. In this work, the error performance of burst-mode receivers has been analyzed based on the combined affect of the random Gaussian noise and the charging/discharging parameters of the receivers. The effect of finite extinction ratio and dc threshold offset voltage is not considered. In future work, a combined study of all effects i.e., random Gaussian noise, the charging/discharging parameters, finite extinction ratio, and dc threshold offset voltage can be achieved. If the work performs experimentally, there is probability of more distortion and interference in burst-mode receiver.

References [1] H. Nishizawa and Y. Yamada, BDesign of a 10-Gb/s burst-mode optical packet receiver and its demonstration in a WDM optical switching network,[ J. Lightw. Technol., vol. 20, no. 7, pp. 1078–1083, Jul. 2002. [2] Y. Ota and R. G. Swartz, BBurst mode compatible optical receiver with large dynamic range,[ J. Lightw. Technol., vol. 8, no. 12, pp. 1897–1903, Dec. 1990. [3] C. Su, L. K. Chen, and K. W. Cheung, BDC-1 Gb/s burst-mode compatible receiver for optical bus application,[ J. Lightw. Technol., vol. 10, no. 2, pp. 244–249, Feb. 1992. [4] L. M. Lunardi, S. Chandrasekhar, R. G. Swartz, R. A. Hamm, and G. J. Qua, BHigh-speed burst-mode OEIC photo receiver using InP/InGaAs hetero junction bipolar transistors,[ in Proc. OFC, San Jose, CA, 1994, pp. 30–31, Paper TuH-2. [5] C. A. Eldering, BTheoretical determination of sensitivity penalty of burst mode: Fiber optic receiver,[ J. Lightw. Technol., vol. 11, no. 12, pp. 2145–2149, Dec. 1993. [6] C. Su, L. K. Chen, and K. W. Cheung, BBER performance of digital optical burst-mode receiver in TDMA all optical multiaccess networks,[ IEEE Photon. Technol. Lett., vol. 7, no. 1, pp. 132–134, Jan. 1995. [7] P. M. Valdes, BPerformance of optical direct receivers using noise corrupted decision threshold,[ J. Lightw. Technol., vol. 13, no. 11, pp. 2202–2214, Nov. 1995. [8] T. Bakker, BDecision threshold based on dynamic offset compensation for burst-mode receiver,[ in Proc. 27th Eur Conf. Opt. Comm., 2001, pp. 222–223.

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[9] R. G. Swart, BA burst-mode, packet capable and automatic dark level compensation for optical bus communication,[ in VLSI Symp. Tech Dig., 1993, pp. 67–68. [10] M. S. Leeson, BCalculation of sensitivity penalty for optically pre amplified burst mode receivers using Fabry–Perot filters,[ Electron. Lett., vol. 34, no. 11, pp. 1121–1122, May 1998. [11] Seo, BA 1.25 Gb/s high sensitive peak detector in optical burst-mode receiver using a 0.18 m CMOS technology,[ in Proc. ICCT, 2003, pp. 644–646. [12] S. Brigati, BA SiGe BiCMOS burst-mode 155-Mb/s receiver for PON,[ IEEE J. Solid-State Circuits, vol. 37, no. 7, pp. 887–897, Jul. 2002. [13] B. C. Thomsen, BOptically equalized 10 Gb/s digital burst mode receiver for dynamic optical networks,[ Opt. Express, vol. 15, no. 15, pp. 9520–9526, Jul. 2007. [14] Optical Zonu Corp. [Online]. Available: www.opticalzonu.com [15] Info-Telcom Systems. [Online]. Available: www.oki.com [16] C. Su, BInherent transmission capacity penalty of burst-mode receiver for optical multiaccess networks,[ IEEE Photon. Technol. Lett., vol. 6, no. 5, pp. 664–667, May 1994. [17] C. Su, L. K. Chen, and K. W. Cheung, BTheory of burst mode optical receiver and its application in optical multi-access networks,[ J. Lightw. Technol., vol. 15, no. 4, pp. 590–606, Apr. 1997. [18] C. Lee, H. Kim, S. Kang, and M. S. Lee, BA systematic evaluation on burst-mode data transmission in passive optical access network,[ in Proc. ICCT, Beijing, China, May 5–7, 1996, pp. 578–581.

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