Non-Cooperative Detection of Frequency-Hopped GMSK Signals

Many current and emerging communication signals use Gaussian Minimum Shift Keyed (GMSK), Frequency-Hopped (FH) waveforms to reduce adjacent-channel interference while maintaining Low Probability of Intercept (LPI) characteristics. These waveforms appear in both military (Tactical Targeting Networking Technology, or TTNT) and civilian (Bluetooth) applications. This research develops wideband and channelized radiometer intercept receiver models to detect a GMSK-FH signal under a variety of conditions in a tactical communications environment. The signal of interest (SOI) and receivers have both fixed and variable parameters. Jamming is also introduced into the system to serve as an environmental parameter. These parameters are adjusted to examine the effects they have on the detectability of the SOI. The metric for detection performance is the distance the intercept receiver must be from the communication transmitter to meet a given set of intercept receiver performance criteria (e.g., PFA and PD). It is shown that the GMSK-FH waveform benefits from an increased hop rate, a reduced signal duration, and the introduction of jitter into the waveform. Narrowband jamming is also very detrimental to channelized receiver performance. The intercept receiver benefits from reducing the bandwidth of the channelized radiometer channels, although this requires precise a priori knowledge of the hop frequencies

Present and Future Trends in Military Satellite Communication Systems

Recent years have seen a phenomenal growth in the field of satellite communications. Satcom systems offer many advantages for military applications which include wide area coverage, rapid deployment, flexible networking and long range service to moving platforms like ships, aircraft and vehicles. This paper gives an overview of the special features and future trends in military satcom systems. A brief account of various countermeasures against threats, use of EHF, spread-spectrum techniques and on board processing has also been given. Major technological advances are anticipated in near future to realise high capacity, secure and survivable satcom systems for Defence applications

New Methods for the Detection and Interception of Unknown, Frequency-Hopped Waveforms

Three new methods for the detection and interception of frequency-hopped waveforms are presented. The first method extends the optimal, fixed-block detection method based on the likelihood ratio to a sequential one based on the Sequential Probability Ratio Test (SPRT). The second method is structured around a compressive receiver and is highly efficient yet easily implemented. The third method is based on the new concept of Amplitude Distribution Function (ADF) and results in a detector that is an extension of the radiometer. The first method presents a detector structured to make a decision sequentially, that is, as each data element is collected. Initially, a purely sequential test is derived and shown to require fewer data for a decision. A truncated sequential method is also derived and shown to reduce the data needed for a decision while operating under poor signal-to-noise ratios (SNRs). A detailed performance analysis is presented along with numerical and Monte Carlo analyses of the detectors. The second method assumes stationary, colored Gaussian interference and presents a detailed model of the compressive receiver. A locally optimal detector is developed via the likelihood ratio theory and yields a reference to which previous ad hoc schemes are compared. A simplified, suboptimal scheme is developed that trades off duty cycle for performance, and a technique for estimating hop frequency is developed. The performance of the optimal and suboptimal detectors is quantified. For the suboptimal scheme, the trade-off with duty cycle is studied. The reliability of the hop frequency estimator is bounded and traded off against duty cycle. In the third method, a precise definition of the ADF is given, from which follows a convolutional relationship between the ADFs of signal and additive noise. A technique is given for deconvolving the ADF, with which signal and noise components can be separated. A detection statistic characterized, yielding a framework on which to synthesize a detector. The detector's performance is analyzed and compared with the radiometer

Simulation and Comparison Between Slow and Fast FH/BPSK Spread Spectrum Using Matlab

يتناول البحث  خصائص وتطبيقات  الطيف المنتشر للقفز الترددي FHSS. FHSS هو احد انواع  الاتصالات الراديوية التي يقوم بها المرسل بتغيير تردد الإرسال استنادا إلى تسلسل محدد سلفا. ان FHSS لديها العديد من المزايا مقارنة بوسائل الارسال التقليدية، حيث يمكنها  التغلب على التلاشي، والقنوات متعددة المسارات والتدخلات. ومن ثم يصبح اعتراضها صعبا. ان الخاصية الامنية هذه جعلت منه ان يكون نظاما مفضلا في التطبيقات العسكرية. وفي جانب المستقبل، يتم إزالة تشكيل الإشارة بواسطة إشارة الموجة الحاملة نفسها التي يتغير ترددها وفقا لنفس تسلسل الشفرة التي يستخدمها المرسل. في هذا البحث تم تناول نوعي  FHSS وهما  السريع والبطيئ. ان طريقة المحاكاة المستخدمة للنوعين انفي الذكر استخدمت  (FH/BPSK) في الماتلاب.ان تتابعية المحاكاة المستخدمة للنوعين البطئي والسريع للقفز العشوائي كانت متشابهة من عدد وقيم الترددات الحاملة  ولنفس نظام (FH/BPSK) .اعتمدت طريقة المقارنة لكلا النوعين على كثافة الموجة الطيفية وقد وجد ان النظام السريع مقاوم للضوضاء اكثر من النوع البطيئ.This paper investigates the properties and applications of Frequency Hopping Spread Spectrum (FHSS).  FHSS is radio communication technique by which the sender of information sends the data on a radio channel, which changes the frequency of transmission based on a predetermined sequence of code. The FHSS has many advantages over traditional modulation methods, it can overcome fading, multipath channels and interferences. Hence the interception becomes difficult. This security feature makes FHSS more preferable for  military applications. At the receiver side, the signal is demodulated by the same carrier signal for which frequency changes by the same code sequences used by the sender. This paper presents two types of FHSS, slow and fast. The  simulation procedures of both types were  implemented and applied on   Frequency Hopping /Binary Phase Shift Keying (FH/BPSK) spread spectrum system using MATLAB. The simulation sequences for fast and slow frequency hopping is the same in number  and frequencies of spreading carriers and both used BPSK traditional modulation type. The  comparison  results  based on their power spectral density   show that the fast frequency hopping is more resistive to noise the slow one

Simulation and Comparison Between Slow and Fast FH/BPSK Spread Spectrum Using Matlab

يتناول البحث  خصائص وتطبيقات  الطيف المنتشر للقفز الترددي FHSS. FHSS هو احد انواع  الاتصالات الراديوية التي يقوم بها المرسل بتغيير تردد الإرسال استنادا إلى تسلسل محدد سلفا. ان FHSS لديها العديد من المزايا مقارنة بوسائل الارسال التقليدية، حيث يمكنها  التغلب على التلاشي، والقنوات متعددة المسارات والتدخلات. ومن ثم يصبح اعتراضها صعبا. ان الخاصية الامنية هذه جعلت منه ان يكون نظاما مفضلا في التطبيقات العسكرية. وفي جانب المستقبل، يتم إزالة تشكيل الإشارة بواسطة إشارة الموجة الحاملة نفسها التي يتغير ترددها وفقا لنفس تسلسل الشفرة التي يستخدمها المرسل. في هذا البحث تم تناول نوعي  FHSS وهما  السريع والبطيئ. ان طريقة المحاكاة المستخدمة للنوعين انفي الذكر استخدمت  (FH/BPSK) في الماتلاب.ان تتابعية المحاكاة المستخدمة للنوعين البطئي والسريع للقفز العشوائي كانت متشابهة من عدد وقيم الترددات الحاملة  ولنفس نظام (FH/BPSK) .اعتمدت طريقة المقارنة لكلا النوعين على كثافة الموجة الطيفية وقد وجد ان النظام السريع مقاوم للضوضاء اكثر من النوع البطيئ.This paper investigates the properties and applications of Frequency Hopping Spread Spectrum (FHSS).  FHSS is radio communication technique by which the sender of information sends the data on a radio channel, which changes the frequency of transmission based on a predetermined sequence of code. The FHSS has many advantages over traditional modulation methods, it can overcome fading, multipath channels and interferences. Hence the interception becomes difficult. This security feature makes FHSS more preferable for  military applications. At the receiver side, the signal is demodulated by the same carrier signal for which frequency changes by the same code sequences used by the sender. This paper presents two types of FHSS, slow and fast. The  simulation procedures of both types were  implemented and applied on   Frequency Hopping /Binary Phase Shift Keying (FH/BPSK) spread spectrum system using MATLAB. The simulation sequences for fast and slow frequency hopping is the same in number  and frequencies of spreading carriers and both used BPSK traditional modulation type. The  comparison  results  based on their power spectral density   show that the fast frequency hopping is more resistive to noise the slow one

Design and FPGA Implementation of Channelizer & Frequency Hopping for Advanced SATCOM System

Advanced satellite communication systems should be capable of preventing unauthorized access or exploitation of communication services by adversaries. This can be achieved by use of wideband multi -channel digital transceivers which employ channelizer to extract the channel of interest from digitized RF bands for further baseband processing. Various anti-jamming techniques like Frequency hopping are used to prevent the systems from intentional jamming by the hostile systems. This paper presents an efficient channelizer architecture which supports wideband as well as narrowband channels with programmable channel bandwidth followed by frequency hopping for the proposed SATCOM system. The target design is a flexible channelization unit which divides the incoming data links of 11 MHz bandwidth into two data links in granularity of 0.5 MHz depending upon user requirements. First link is further sub-channelized into two sub-links each having a bandwidth of 25 KHz that is frequency hopped at a user programmable rate with desired random sequence. The same channelizer can be well applicablein any software defined radio receiver platforms due to flexibility of the design. Proposed design is tested on target hardware XilinxVirtex-IV FPGA xc4vsx35-10ff668. The design and implementation of the channelizer and frequency hopping technique arediscussed in detail

Performance Study of Hybrid Spread Spectrum Techniques

This thesis focuses on the performance analysis of hybrid direct sequence/slow frequency hopping (DS/SFH) and hybrid direct sequence/fast frequency hopping (DS/FFH) systems under multi-user interference and Rayleigh fading. First, we analyze the performance of direct sequence spread spectrum (DSSS), slow frequency hopping (SFH) and fast frequency hopping (FFH) systems for varying processing gains under interference environment assuming equal bandwidth constraint with Binary Phase Shift Keying (BPSK) modulation and synchronous system. After thorough literature survey, we show that hybrid DS/FFH systems outperform both SFH and hybrid DS/SFH systems under Rayleigh fading and multi-user interference. Also, both hybrid DS/SFH and hybrid DS/FFH show performance improvement with increasing spreading factor and decreasing number of hopping frequencies