Nowadays most communication networks like GSM, WLan or WiMAX are based on pre-existing infrastructure. These infrastructures are complicated, costly and difficult to deploy in very short time. Whereas Wireless Ad Hoc Networks are infrastructure-free self organizing networks which consist of co-operating nodes. These networks are highly desirable for various emerging applications for military and to extend the range and capacity of infrastructure based wireless networks. One critical issue that we face in Ad Hoc Network is the problem of scheduling. Scheduling algorithms in an Ad Hoc Network allows the nodes to share the wireless channel efficiently. But on the other hand, the scheduling algorithm needs to be easily implementable in a distributed fashion with little, if any, coordination between nodes in the network. Spread spectrum technologies allow interference averaging and therefore are employed in Ad Hoc networks. There are two major types of spread spectrum physical layer, which are frequency hopping (FH) spread spectrum and direct sequence (DS) spread spectrum. FH-CDMA divides the bandwidth into M sub channels, the receiver only sees the interference from the transmitter side which is on the same sub channel whereas in DS-CDMA we increase the spreading code M to decrease the signal to interference plus noise ratio (SINR) requirement. The purpose of research is to study a hybrid spread spectrum based on physical layer, in which the direct sequence signal is also frequency hoped. The DS will reduce the region of dominating interferes, while frequency hopping will be used within this region intelligently and allow the dominating interferes to transmit on different frequencies. First the system bounds on the transmission capacity of the proposed scheme is evaluated, and than a comparative analysis of different multiple access schemes is done with our proposed model with respect to their transmission capacity to evaluate its performance.

The Global Positioning System (GPS) satellite signals provide not only traditional radionavigation service but inexpensive and convenient radio beacons for signal propagation studies on ionosphere and atmosphere. This thesis describes the development and testing of a specialized GPS sensor which measures, plots and records real-time high-resolution L1 (1575.42MHz) GPS signal strength at a data rate of up to 10Hz. The instrument is based on an open architecture GPS receiver development kit that can be modified and rebuilt. The signal strength is defined as mean-square signal strength in the thesis. The coarse/acquisition code (C/A-code) correlation is applied and the raw correlation data from a GPS correlator chip is obtained to calculate the signal strength. The gain variation of the automatic gain control (AGC) in the GPS signal link is considered, and a model is designed and implemented in data post-processing to reduce the AGC distortion to GPS signal strength measurements. Speed limitation of 1,000 knots and height limitation of 60,000 feet are removed so that it can track spacecraft such as low earth orbit (LEO) satellite. Four testing plans are developed and conducted to test the GPS signal strength sensor. A GPS simulator is used and the testing results prove that the space-borne sensor is fully operational and the signal strength resolution can be smaller than 0.05dB. Additionally, a COM-port-to-TCP/IP GPS simulation remote control gateway is designed and implemented for the senor and the GPS simulator to conduct formation flying. A graphic user interface (GUI) program is also built to retrieve data from a commercial high-performance space-borne GPS receiver for comparison. A Red Hat Linux signal strength sensor based on the National Aeronautics and Space Administration (NASA) PiVoT GPS receiver is achieved by modifications. The NASA PiVoT sensor, working together with the former signal strength sensor and the commercial space-borne GPS receiver, will strengthen our academic research strength in the studies on the ionospheric and atmospheric effects and irregularities which cause GPS signal degradation and scintillations. / Master of Science

Les systèmes de localisations existants présentent des insuffisances au niveau desapplications en environnement indoor. Ces insuffisances se traduisent soit par la non-disponibilité des signaux (le GPS) dans ce type d’environnement, soit par leur manque de précision quand ils sont prévus à cet effet. Ces limites ont motivé la recherche de nouvelles techniques. Les transmissions Ultra-Large Bande (ULB) de par leur singularité en matière de précision et de faible puissance d’émission, s’avèrent être la meilleure réponse à la problématique ci-dessus. Nous avons donc choisi cette technique pour mettre au point un procédé de localisation endogène permettant d’assurer, avec précision, la continuité des services de localisation dans les environnements indoor. Ce procédé s’appuie sur la localisation en trois dimensions (3-D). Il utilise la technique temporelle de différenciation du temps d’arrivée (TDOA). Cette technique permet de mieux tirer profit de la bonne résolution temporelle de l’ULB et de pallier au problème de synchronisation entre l’émetteur et le récepteur. Deux techniques de transmission ULB ont été étudiées : la technique d’accès multiples par séquence directe (DS-CDMA) et la technique d’accès multiples par sauts temporels (TH-CDMA). Une autre étape importante de notre étude a été de développer un algorithme non-itératif de localisation en 3-D pour réduire le temps de calcul. En effet, l’utilisation d’un algorithme non-itératif permet d’optimiser les performances du système en termes de temps de calcul voire de coûts de consommation énergétique. Après l’étude théorique des différents blocs du système, le système a été tout d’abord simulé dans le canal Gaussien (AWGN) et les canaux IEEE.802.15.4a indoor. Il a été ensuite testé dans différents environnements réels de types laboratoires. Les résultats obtenus démontrent que l’utilisation des techniques de transmission basées sur la technologie radio impulsionnelle ULB permet d’obtenir un système de localisation en 3-D avec une précision centimétrique pour les applications indoor. / Existing positioning systems have deficiencies in applications indoor environment. These deficiencies result is the non-availability of signals (GPS) in this type of environment, either by their lack of precision when they are provided for this purpose. These limitations have led to research for novel techniques. Ultra-Wide Band (UWB) transmission techniques due to their uniqueness in terms of fine resolution and low power emission, prove to be the best answer to this problem. So we choose this technique to develop a process to ensure self location, with accuracy, continuity of location services in indoor environments. This method is based on the location in three dimensions (3-D). It uses the Time Difference Of Arrival (TDOA) technique. This technique allows to better take advantage of the high time resolution of the ULB and overcome the problem of synchronization between the transmitter and the receiver. Two UWB transmission techniques were studied: the Direct Sequence multiple access technique (DS-CDMA) and Time Hopping (TH-CDMA) multiple access technique. Another important step in our study was to develop a non-iterative positioning algorithm in 3-D to reduce the computation time. Indeed, using a non-iterative algorithm optimizes system performance in terms of computing time or cost of energy consumption. After the theoretical study of the system, the proposed positioning system was firstly simulated in Additive White Gaussian Noise (AWGN) channel and indoor IEEE.802.15.4a channels. It was then tested in various real environments types laboratories. The results obtained show that using UWB impulse radio technology transmission techniques allows to achieve a high accuracy 3-D location system in order of centimeter for applications in indoor environments.

In the context of broadband wireless communications using code division multiple access (CDMA), the main multiple access (MA) options include single-carrier direct sequence CDMA (SC-DS-CDMA) using time-domain direct sequence spreading [1, p. 728], multicarrier CDMA (MC-CDMA) using frequency-domain spreading [2, 3] and multicarrier DS-CDMA (MC-DS-CDMA) using time-domain direct sequence spreading of the individual sub-carrier signals [4, 5]. It was shown in [6] that MC-DS-CDMA has the highest degrees of freedom in the family of CDMA schemes that can be beneficially exploited during the system design and reconfiguration procedures. An amalgam of MC-CDMA and MC-DS-CDMA known as time and frequency domain spreading (TF-domain spreading) MC-DS-CDMA was proposed in [6]. TF-domain spreading MC-DS-CDMA has several benefits over conventional MC-DS-CDMA with regard to both capacity and performance [7]. However, in contrast to conventional MC-DS-CDMA, TF-domain spreading MC-DS-CDMA introduces MUI, which necessitates the use of joint detection at the receiver. Recently, multiple input multiple output (MIMO) or multi-antenna TF-domain spreading MC-DS-CDMA schemes have been proposed in the literature that e ciently exploit both the spatial and frequency diversity available in MIMO frequency-selective channels [8, 9]. Although an extensive amount of research has been done on single and multi-antenna TF-domain spreading MC-DS-CDMA schemes that achieve both spatial and frequency diversity in frequency-selective slow fading channels [6–9], very little research considers the time-selectivity of the wireless channels encountered. Thus, the above-mentioned schemes may not be su ciently e cient, when communicating over wireless channels exhibiting both frequency-selective and time-selective fading. There are very few MC-DS-CDMA schemes in the literature that consider the time-selectivity of the wireless channels encountered. This study considers the design of single and multi-antenna TF-domain spreading MC-DS-CDMA, for frequency-selective block-fading channels, which are capable of exploiting the full diversity available in the channel (i.e. spatial, frequency and temporal diversity), using various methods of joint detection at the receiver. It has been shown that the diversity gain in block-fading channels can be improved by coding across multiple fading blocks [10–12]. Single-antenna TF-domain spreading MC-DS-CDMA is considered for the quasi-synchronous uplink channel, and multi-antenna TF-domain spreading MC-DS-CDMA is considered for the synchronous downlink channel. Numerous simulated bit error rate (BER) performance curves, obtained using a triply selective MIMO channel platform, are presented in this study using optimal and sub-optimal joint detection algorithms at the receiver. In addition, this study investigates the impact of spatial correlation on the BER performance of the MC-DS-CDMA schemes considered. From these simulated results, one is able to conclude that TF-domain spreading MC-DS-CDMA designed for frequency-selective block-fading channels performs better than previously proposed schemes designed for frequency-selective slow fading channels, owing to the additional temporal diversity exploited under the block-fading assumption. AFRIKAANS : In die konteks van bre¨eband- draadlose kommunikasie deur die gebruik van kodeverdelingveelvuldige toegang (KVVT) behels die belangrikste veelvuldigetoegang- (VT) opsies enkel-draer direkte-sekwensie KVVT (ED-DS-KVVT), deur die gebruik van tyd-domein direkte sekwensie-verspreiding [1, p. 728], veelvuldigedraer-KVVT (VD-KVVT) deur die gebruik van frekwensiedomein-verspreiding [2, 3] en VD-DS- KVVT deur die gebruik van tyd-domein direkte sekwensie-verspreiding van die individuele sub-draerseine [4, 5]. Daar is in [6] aangetoon dat VD-DS-KVVT die hoogste vlakke van vryheid in die familie KVVT-skemas het wat voordelig benut kan word gedurende sisteemontwerp en rekonfigurasieprosedures. ’n Amalgaam van VD-KVVT en VD-DS-KVVT bekend as tyd-en-frekwensiedomeinverspreiding (TF-domeinverspreiding) VD-DS-KVVT is voorgestel in [6]. TF-domeinverspreiding VD-DS-KVVT het verskeie voordele bo konvensionele VD-DS-KVVT wat sowel kapasiteit as werkverrigting betref [7]. In teenstelling met konvensionele VD-DS-KVVT benut TF-domeinverspreiding VD-DS-KVVT multi-gebruiker-interferensie, wat die gebruik van gesamentlike opsporing by die ontvanger noodsaak. In die onlangse verlede is in die literatuur veelvuldige-inset-veelvuldige-uitset- (VIVU) of veelvuldige-antenna TF-omeinverspreiding VD-DS-KVVT-skemas voorgestel wat sowel die ruimtelike as frekwensiediversiteit wat in VIVU frekwensie-selektiewe kanale beskikbaar is, e ektief gebruik [8, 9]. Hoewel uitgebreide navorsing onderneem is oor enkel- en multi-antenna TF-domeinverspreiding VD-DS-KVVT-skemas wat sowel ruimtelike as frekwensie diversiteit in frekwensie-selektiewe stadig deinende kanale bereik [6–9], oorweeg baie min navorsing die tyd-selektiwiteit van die draadlose kanale wat betrokke is. Bogenoemde skemas mag dus nie e ektief genoeg wees nie wanneer kommunikasie plaasvind oor draadlose kanale wat sowel frekwensie-selektiewe as tyd-selektiewe wegsterwing toon. Baie min VD-DS-KVVT-skemas in die literatuur skenk aandag aan die tyd-selektiwiteit van die betrokke draadlose kanale. Die studie ondersoek die ontwerp van enkel- en multi-antenna TF-domeinverspreiding VD-DS-KVVT vir frekwensie-selektiewe blokwegsterwingkanale, wat in staat is om die volle diversiteit wat in die kanaal beskikbaar is, te benut (i.e. ruimtelike, frekwensie- en tyddiversiteit), deur die gebruik van verskeie metodes van gesamentlike opsporing by die ontvanger. Daar is aangetoon dat die diversiteitwins in blokwegsterwingkanale verbeter kan word deur kodering oor veelvuldige deinende blokke [10–12]. Enkel-antenna TF-domeinverspreiding VD-DS-KVVT word oorweeg vir die kwasi-sinchroniese opverbinding-kanaal, en multi-antenna TF-domeinverspreiding VD-DS-KVVT vir die sinchroniese afverbinding-kanaal. Talryke gesimuleerde bisfouttempo (BFT) werkverrigtingkurwes wat verkry is deur die gebruik van ’n drie-voudige selektiewe VIVU-kanaalplatform, word in hierdie studie aangebied, deur die gebruik van optimale en sub-optimale gesamentlike opsporingsalgoritmes by die ontvanger. Daarbenewens ondersoek hierdie studie die impak van ruimtelike korrelasie op die BFT-werkverrigring van die VD-DS-KVVT-skemas wat oorweeg word. Uit hierdie gesimuleerde resultate is dit moontlik om tot die gevolgtrekking te kom dat TF-domeinverspreiding VD-DS-KVVT wat ontwerp is vir frekwensie-selektiese blokwegsterwingkanale beter werkverrigting toon as vroe¨er voorgestelde skemas wat ontwerp is vir frekwensie-selektiewe stadig deinende kanale, te danke aan die ekstra tyddiversiteit wat deur die blokwegsterwing-aanname benut word. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

In general, PN code synchronization consists of two steps: PN code acquisition (coarse alignment) and PN code tracking (fine alignment), to estimate the delay offset between received and locally generated codes. Recently, the schemes with a joint adaptive process of PN code acquisition and the weight coefficients of smart antenna have been proposed for improving the received signal-to-interference-plus-noise ratio (SINR) and simultaneously achieving better mean-acquisition-time (MAT) performance in direct-sequence code-division multiple access (DS-CDMA) systems. In which, the setting of the threshold plays an important role on the MAT performance. Often, the received SINR is varying, using the fixed threshold acquisition algorithms may result in undesirable performance. To improve the above problem, in this thesis, a new adaptive threshold scheme is devised in a joint adaptive code acquisition and beam-forming DS-CDMA receiver for code acquisition under a fading multipath and additive white Gaussian-noise (AWGN) channels. The basic idea of this new adaptive threshold scheme is to estimate the averaged output power of smart antenna to scale a reference threshold for each observation interval, such that it can approximately achieve a constant false alarm rate (CFAR) criteria. The system probabilities of the proposed scheme are derived for evaluating MAT under a slowly fading two-paths channels. Numerical analyses and simulation results demonstrate that the proposed adaptive threshold scheme does achieve better performance, in terms of the output SINR, the detection probability and the MAT, compared to a fixed threshold method.

Direct-Sequence Code Division Multiple Access (DS-CDMA), over the last few years, has become a popular technique and finds a place in many modern communication systems. The performance of this technique is closely linked to the signature (or spreading) sequences employed in the system. In the past, there have been many successful attempts by research groups to construct families of signature sequences that offer the potential gains promised by theoretical bounds. In this thesis, we present constructions of families of signature sequences over the AM-PSK and QAM alphabet with low correlation. In this thesis, we construct a family of sequences over the 8-ary AM-PSK constella- tion, Family AOpt(16) that is asymptotically optimal with respect to the Welch bound on maximum magnitude of correlation for complex sequences. The maximum magnitude of correlation for this family, θmax, is upper bounded by √N , where N is the period of the sequences. The 8-ary AM-PSK constellation is a subset of the 16-QAM constellation. We also construct two families of sequences over 16-QAM, Family A16A, and Family A16,B , with the maximum magnitude of correlation upper bounded by √2√N . We construct a family, A(M 2), of sequences over the 2m+1-ary AM-PSK constellation of period N = 2r- 1 and family size (N + 1)/2m-1 . The 2m+1-ary AM-PSK constellation is a subset of the M 2-QAM constellation with M =2m . The maximum nontrivial normalized correlation parameter is bounded above by θmax < a √N where a ranges from 1.34 in the case of M 2 = 16 to √5 for large m. Apart from low correlation values, the family possesses several interesting and useful features. In Family A(M 2), users have the ability to transmit 2m bits of data per period of the spreading sequence. The sequences in Family A(M 2) are balanced; all points from the 2m+1-ary AM-PSK constellation occur approximately equally often in sequences of long period. The Euclidean distance between the signals assigned to a particular user in A(M 2), corresponding to different data symbols, is larger than the corresponding value for the case when 2m+1-PSK modulation and spreading is used. Perhaps most interestingly, Family A(M 2) permits users on the reverse link of a CDMA system to communicate asynchronously at varying data rates by switching between different QAM constellations. Family A(M 2) is compatible with QPSK sequence families S(p) in the sense that the maximum correlation magnitude is increased only slightly if one adds sequences from (p) S(p)\ S(0) to Family A(M 2). We also construct families of sequences over AM-PSK that tradeoff data rate per sequence period and θmax for a given family size. We have extended the construction of sequences over AM-PSK constellation to construct sequences over the M 2-QAM constellation for M =2m . The QAM sequence families, Families (AM 2), have size, data rate and minimum squared Euclidean distance same as the corresponding AM-PSK construction but have higher values of θmax. Also included in the thesis are constructions for large families of sequences over the M 2-QAM alphabet.

Pour certaines applications, le besoin de recourir à des communications furtives est essentiel, notamment pour des transmissions militaires. Le canal acoustique sous-marin est un milieu naturellement très bruité. Il est sujet à de nombreuses sources de bruits, de réfections et de réfractions des ondes acoustiques qui font apparaître des trajets multiples. En tenant compte de l'aspect multi-trajets du canal sous-marin et de l'émission d'ondes acoustiques peu détectables pour les besoins de notre application, nous avons proposé un système de transmission basé sur l'étalement de spectre par séquence directe et de l'accès multiple à répartition par codes. Nous avons présenté les récepteurs adaptés à cette méthode de transmission et nous avons étudié leurs performances pour des canaux multi-trajets avec de l'interférence multi-utilisateurs. La structure de ces récepteurs permet à la fois d'estimer les paramètres des canaux multi-trajets par l'application d'un banc de filtres adaptés aux signaux d'étalements des différents utilisateurs et de profiter de la diversité spatiale du canal sous-marin grâce à une recombinaison cohérente de l'énergie des différents trajets, après l'estimation du canal. L'estimation des temps des retards et des amplitudes sont obtenues à la sortie des filtres adaptés aux signaux des utilisateurs, au rythme symbole. Nous montrons qu'il est possible d'améliorer les performances du système en appliquant une méthode de suppression successive de l'interférence. Les résultats obtenus montrent que le système proposé permet de garantir de très bonnes performances à des rapports signal à bruit très faible, avec une convergence rapide en seulement trois étages d'itérations. Enfin, nous proposons d'introduire un codage de canal afin d'améliorer les performances en termes de robustesse grâce à des codes correcteurs d'erreurs. Certains des algorithmes développés au cours de cette thèse ont finalement été testés sur des données réelles, ce qui a permis notamment de démonter en pratique les bonnes performances du système. Le dépouillement des données réelles a permis de mettre en évidence le profil des canaux multi-trajets dans les zones d'expérimentation. Comme l'estimation du canal et la détection des signaux peuvent être coûteuses en temps de calcul, nous proposons de tenir compte du profil réel des canaux multi-trajets et de réduire le nombre des trajets à considérer selon la puissance du trajet principal d'une manière adaptative.

Les systèmes de localisations existants présentent des insuffisances au niveau desapplications en environnement indoor. Ces insuffisances se traduisent soit par la non-disponibilité des signaux (le GPS) dans ce type d'environnement, soit par leur manque de précision quand ils sont prévus à cet effet. Ces limites ont motivé la recherche de nouvelles techniques. Les transmissions Ultra-Large Bande (ULB) de par leur singularité en matière de précision et de faible puissance d'émission, s'avèrent être la meilleure réponse à la problématique ci-dessus. Nous avons donc choisi cette technique pour mettre au point un procédé de localisation endogène permettant d'assurer, avec précision, la continuité des services de localisation dans les environnements indoor. Ce procédé s'appuie sur la localisation en trois dimensions (3-D). Il utilise la technique temporelle de différenciation du temps d'arrivée (TDOA). Cette technique permet de mieux tirer profit de la bonne résolution temporelle de l'ULB et de pallier au problème de synchronisation entre l'émetteur et le récepteur. Deux techniques de transmission ULB ont été étudiées : la technique d'accès multiples par séquence directe (DS-CDMA) et la technique d'accès multiples par sauts temporels (TH-CDMA). Une autre étape importante de notre étude a été de développer un algorithme non-itératif de localisation en 3-D pour réduire le temps de calcul. En effet, l'utilisation d'un algorithme non-itératif permet d'optimiser les performances du système en termes de temps de calcul voire de coûts de consommation énergétique. Après l'étude théorique des différents blocs du système, le système a été tout d'abord simulé dans le canal Gaussien (AWGN) et les canaux IEEE.802.15.4a indoor. Il a été ensuite testé dans différents environnements réels de types laboratoires. Les résultats obtenus démontrent que l'utilisation des techniques de transmission basées sur la technologie radio impulsionnelle ULB permet d'obtenir un système de localisation en 3-D avec une précision centimétrique pour les applications indoor.

The subject of this work deals with the problem of channel estimation for CDMA systems. This method of multiple access when individual users share the same full bandwidth simultaneously and are differentiated with any of pseudorandom sequences, is now the most perspective method. That is proved by its wide implementation in mobile networks of the third generation and higher systems. This work describes basic theory principles of spread spectrum, above all DS-CDMA (Direct Sequence-CDMA) and furthermore some phenomena of radio wireless channel that affect changes in transmitted signal in its way from transmitter to receiver. Terms of fading, multipath propagation, loss, refraction, scattering of the wave and Rice and Rayleigh probability density functions are mentioned. The third chapter deals with yet known and used capabilities of channel estimation. Differences, advantages and disadvantages of so-called blind estimation or training-based estimation are discussed. Two algorithms: LS method and sliding correlator are analyzed in more detail. There is also description of their simulations in Matlab and some results of these simulations are discussed. The last chapter deals with comparison of main characteristics and achievable accuracy of wireless channel impulse response estimation by both methods, and their possible utilization in real live.