In this study, we propose and demonstrate a flat-top birefringent optical interleavers utilizing a new ring-cavity as a phase-shift element. The uniform performance over entire C-band is a result of the unique ring-cavity architecture which utilizes Fresnel reflections of the prism-air interface to provide the partial reflections. Unlike dielectric mirrors with thin-film coatings, the reflectivities of Fresnel reflection are insensitive to wavelength variations in the transmission band. In the ring-cavity based birefringent interferometer (RCBI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 17.5 GHz (70% of the channel spacing), a 25-dB stopband greater than 17.5 GHz (70% of the channel spacing), a channel isolation better than 28 dB, and insertion loss lower than 2.2 dB. In the ring-cavity based birefringent Sagnac interferometer (RCBSI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 18.1 GHz (72.5% of the channel spacing), a 25-dB stopband greater than 18.1 GHz (72.5% of the channel spacing), a channel isolation better than 36 dB, and insertion loss lower than 1.5 dB. The RCBSI interleaver requires less number of optical components and hence results in more than 0.7 dB and 2.5% improvements in the insertion loss and band utilization, respectively, when compared to the RCBI interleaver. Therefore, the novel RCBSI interleaver can be used in dense wavelength division multiplexing (DWDM) applications.

In this dissertation, we study the fabrication and performance of fiber coupler, add/drop filter module, and flat-top interleaver for use in dense wavelength division multiplexing (DWDM) systems. In the low loss fused biconical taper coupler (FBTC), an optimum approach for fabrication of FBTC is a lower filament speed, a higher gas flow rate, and a longer pulling length. By applying this optimum approach that the FBTCs with low loss of 0.13 dB and small taper angle of 20o have been fabricated successfully. In the add/drop filter module, the module-insertion loss difference (0.3 dB) and angular tilt misalignment (0.05o) are found after undergoing 42 temperature cycles for the imperfect soldering process. We present our experimental results of a flat-top 50 GHz optical interleaver using two Gires-Tournois Etalons (GTEs) as phase dispersive mirrors in a Michelson interferometer. The spectral characteristics of the interleaver in a 50 GHz channel spacing application exhibit a 0.5 dB passband larger than 43.8 GHz (88% of the spacing), a 25 dB stopband greater than 40 GHz (80% of the spacing), and a channel isolation higher than 35 dB. The result shows that the interleaver interferometer with novel GTE technique can simultaneously produce a 0.5 dB passband and a 25 dB stopband wider than other interferometer techniques.

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In recent years, several studies and simulations have been made on changing the current Radio Access Network (RAN) architecture into a more centralized access network where the base band processing is done in a central oce (CO) instead of out by the antenna site. This new architecture is denoted as the mobile fronthaul and is planned to be in use for the coming 5G network. The studies that have been made so far suggest that the new architecture can reduce cost, power usage and latency which are important factors regarding environmental, economical and data transmission issues. Furthermore, the new architecture allows a smarter distribution of data for each sector covered by the antennas, reducing redundant data transmission and thus increases the data eciency. The disadvantage or challenge however is that some of the optical components will be transferred from the currently controlled environment in the CO to an uncontrolled outdoor environment at the antenna site, which may generate risks as these components may be sensitive to especially changes in temperature. In this master thesis, the optical performance of four di erent passive lter setups, using a thin lm lter (TFF), an arrayed waveguide grating (AWG) and an interleaver, has been studied and compared in order to nd the most suitable lter setup for the mobile fronthaul. These optical parameters include insertion loss, isolation, crosstalk, 3 dB passband, center wavelength drift and also bit error-rate (BER) which have all been measured over a temperature interval of -40-85oC. Moreover, the measurement results have been compared with results from simulations done with VPItransmissionmaker. From the measurement results, the TFF had a better optical performance and reliability compared to the AWG mainly due to a higher isolation and a lower BER penalty of 0.2 dB compared to 0.5-1.5 dB for the AWG. Considering data capacity and economical aspects for a more realistic mobile fronthaul scenario with 80 channels using dense wavelength division multiplexing (DWDM) however, the AWG connected to the interleaver is more benecial without risking negative a ects on trac performance. / Under senare år har flera studier och simulationer utförts med syfte att ändra arkitekturen på dagens radioaccess-nätverk till ett mer centraliserat nätverk där basbandsprocesseringen sker i en central nod istället för ute vid antennen och radiomasterna. Denna nya arkitektur kallas mobile fronthaul och planeras att realiseras till 5G-nätet. De studier som har gjorts hittills indikerar på att den nya arkitekturen kan minska ekonomiska kostnader, elanvändningen och latens vilka är viktiga faktorer som bland annat rör miljö-, ekonomi och kapacitetrelaterade områden. Dessutom kan data fördelas på ett smartare sätt över alla delområden som antennerna täcker vilket minskar redundant datatrafik och därmed ökar den effektiva mängden data som skickas ut. Problemet eller utmaningen är att vissa optiska komponenter behöver flyttas från en nuvarande kontrollerad miljö till en okontrollerad utemiljö vid radiomasterna vilket kan medföra risker då dessa komponenter främst kan vara väldigt temperaturkänsliga. Inom detta examensarbete har optisk prestanda studerats, analyserats och jämförts mellan fyra olika filterkonstellationer bestående av ett tunnfilmsfilter, ett AWG-filter och en interleaver med syfte att finna vilken konstellation som passar bäst för mobile fronthaularkitekturen. De optiska parametrarna består av insertionsförluster, isolation, överhörningsinterferens, 3 dB-passband, centervåglängdsdrift samt bitfelsgrad vilka alla har blivit undersökta över ett temperaturintervall på -40-85oC. Utöver detta så har mätresultaten jämförts med simulationer gjorda med VPItransmissionmaker. Utifrån mätresultaten kunde det konstateras att tunnfilmfiltret hade bättre optiska egenskaper och även högre trovärdighet jämfört med AWG-filtret främst på grund av en högre isolation och lägre bitfelsgradsstraff på 0.2 dB jämfört med 0.5-1.5 dB för AWG-filtret. Om en endast avväger datakapacitet och ekonomiska aspekter för ett mer realistiskt scenario för mobile fronthaul med 80 DWDM-kanaler så är AWG-filtret tillsammans med interleavern mer foördelaktig att välja utan att riskera några negativa påverkningar på trafikprestandan.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The turbo code is a block code even though a convolutional encoder is used to construct codewords. Its performance depends on the code word length. Since the invention of the turbo code in 1993, most of the bit error rate (BER) evaluations have been performed using large block sizes, i.e., sizes greater than 1000, or even 10,000. However, for telemetry and command, a relatively short message (<500 bits) may be used. This paper investigates the turbo-coded BER performance for short packets. Fading channel is also considered. In addition, biased channel side information is adopted to improve the performance.

A low-complexity method of interleaver design, sub-vector interleaving, for both parallel and serially concatenated convolutional codes (PCCCs and SCCCs, respectively) is presented here. Since the method is low-complexity, it is uniquely suitable for designing long interleavers. Sub-vector interleaving is based on a dynamical system representation of the constituent encoders employed by PCCCs and SCCCs. Simultaneous trellis termination can be achieved with a single tail sequence using sub-vector interleaving for both PCCCs and SCCCs. In the case of PCCCs, the error floor can be lowered by sub-vector interleaving which allows for an increase in the weight of the free distance codeword and the elimination of the lowest weight codewords generated by weight-2 terminating input sequences that determine the error floor at low signal-to-noise ratios (SNRs). In the case of SCCCs, sub-vector interleaving lowers the error floor by increasing the weight of the free distance codewords. Interleaver gain can also be increased for SCCCs by interleaving the lowest weight codewords from the outer into non-terminating input sequences to the inner encoder. Sub-vector constrained S-random interleaving, a method for incorporating S-random interleaving into sub-vector interleavers, is also proposed. Simulations show that short interleavers incorporating S-random interleaving into sub-vector interleavers perform as well as or better than those designed by the best and most complex methods for designing short interleavers. A method for randomly generating sub-vector constrained S-random interleavers that maximizes the spreading factor, S, is also examined. The convergence of the turbo decoding algorithm to maximum-likelihood decisions on the decoded input sequence is required to demonstrate the improvement in BER performance caused by the use of sub-vector interleavers. Convergence to maximum-likelihood decisions by the decoder do not always occur in the regions where it is feasible to generate the statistically significant numbers of error events required to approximate the BER performance for a particular coding scheme employing a sub-vector interleaver. Therefore, a technique for classifying error events by the mode of convergence of the decoder is used to illuminate the effect of the sub-vector interleaver at SNRs where it is possible to simulate the BER performance of the coding scheme.

Diversity transmission is an effective technique to combat fading channels and this thesis introduces two main ideas. Firstly, a novel precoding technique is proposed to achieve diversity transmission and improve bit error rate (BER) performance over the existing linear constellation precoding (LCP) techniques. Experimental and theoretical results are presented to show that the proposed precoding schemes can outperform the existing LCP schemes in various fading channels and additive white Gaussian noise channels. Secondly, an interleaving technique to further improve the BER performance is proposed. The proposed diversity transmission techniques are implemented for both single-carrier and orthogonal frequency division multiplexing (OFDM) systems. The second part of the thesis focuses on the pairwise error probability analysis of the proposed and LCP schemes when receivers have imperfect channel state information (CSI). The BER performance of the proposed precoding and interleaver scheme are investigated in OFDM systems with minimum mean square error channel estimators and single-carrier systems with basis expansion model based channel estimators. It is demonstrated that while precoding schemes designed for receivers with perfect CSI yield near-optimum BER performance in the former system, the proposed phase-shift keying based precoding schemes perform well in the latter system. In both cases, the proposed precoding scheme, combined with the novel interleaving technique, outperforms the existing LCP schemes.

Diversity transmission is an effective technique to combat fading channels and this thesis introduces two main ideas. Firstly, a novel precoding technique is proposed to achieve diversity transmission and improve bit error rate (BER) performance over the existing linear constellation precoding (LCP) techniques. Experimental and theoretical results are presented to show that the proposed precoding schemes can outperform the existing LCP schemes in various fading channels and additive white Gaussian noise channels. Secondly, an interleaving technique to further improve the BER performance is proposed. The proposed diversity transmission techniques are implemented for both single-carrier and orthogonal frequency division multiplexing (OFDM) systems. The second part of the thesis focuses on the pairwise error probability analysis of the proposed and LCP schemes when receivers have imperfect channel state information (CSI). The BER performance of the proposed precoding and interleaver scheme are investigated in OFDM systems with minimum mean square error channel estimators and single-carrier systems with basis expansion model based channel estimators. It is demonstrated that while precoding schemes designed for receivers with perfect CSI yield near-optimum BER performance in the former system, the proposed phase-shift keying based precoding schemes perform well in the latter system. In both cases, the proposed precoding scheme, combined with the novel interleaving technique, outperforms the existing LCP schemes.

A partially parallel reconfigurable channel switch is constructed for use in DFBR. Its permutation can be changed while running without any interruption in the streams of data. Three approaches are tried: one based on asorting network, one based on memories and multiplexers and one based on a Clos network. Variants with the pattern stored in memories and in shift registers are tried. They are implemented in automatically generated Verilog and synthesized for an FPGA. Their cost in terms of area use, memory use and maximum clock frequency is compared and the results show that the Clos based approach is superior in all aspects and that pattern data should not be saved in shift registers. The work is open source and available for download at https://github.com/channelswitch/channelswitch. / En delvis parallel och delvis seriell kanalswitch för användning inom DFBR skapas. Dess permutation kan ändras medan den kör utan avbrott i dataströmmen. Tre alternativ undersöks: ett baserat ett sorteringsnätverk, ett baserat på minnen och multiplexrar och ett som baseras på Clos-nätverk. Versioner med mönsterdata sparad i skiftregister och i minnen prövas. De implementeras i automatiskt genererad Verilog och synthesiseras för en FPGA. Deras kostnad i areaanvändning, minnesanvändning och maximal klockfrekvens jämförs. Resultaten visar i princip att Clos-nätverken är bäst i alla avseenden och att mönsterdata ska sparas i RAM-minnen och inte i skiftregister. Arbetet är open source och kan laddas ner från https://github.com/channelswitch/channelswitch.