Modulation Code Division Multiple Access Research Articles

Sub-Nyquist Sampling Receiver for Overlay Cognitive Radio Users

The secondary users (SUs) in cognitive radio (CR) networks exploit the underutilized radio spectrum of the primary networks. In overlay CR systems, transmit waveforms can be designed either in orthogonal frequency-division multiplexing or in multicarrier code division multiple access modulation formats by deactivating subcarriers corresponding to primary users’ frequency bands to avoid interference. Transmissions of these overlay CR waveforms are expected to be extremely wideband, occupying up to 1 GHz of bandwidth. As reception of such wideband signals requires very high Nyquist sampling rates, we propose to employ a sub-Nyquist sampling front end. The proposed sub-Nyquist sampling receiver collects as coherently as possible all the SU signals spread across the entire frequency span of interest. Our theoretical analysis and simulation results demonstrate that the proposed receiver performs very close to the Nyquist rate receiver with significantly reduced complexity.

Errata: High precision three-dimensional iterative indoor localization algorithm using code division multiple access modulation based on visible light communication

Errata: High precision three-dimensional iterative indoor localization algorithm using code division multiple access modulation based on visible light communication

High precision three-dimensional iterative indoor localization algorithm using code division multiple access modulation based on visible light communication

To solve the problem of positioning accuracy affected by mutual interference among multiple reference points in the traditional visible light communication positioning system, an iterative algorithm of received signal strength (RSS) based on code division multiple access (CDMA) coding is proposed. Every light-emitting diode (LED) source broadcasts a unique CDMA modulation identification (ID) code, which is associated with geographic position. The mobile terminal receives a mixed light signal from each LED reference point. By using the orthogonality of the spreading codes, the corresponding ID position information and the intensity attenuation factor of each LED reference point source can be available. According to the ID information and signal attenuation intensity, the location area of each LED and the distance between the receiver end and each LED can be determined. The three-dimensional (3-D) position of the receiver can be obtained by using the iterative algorithm of RSS triangulation. The experimental results show that the proposed algorithm can achieve a positioning accuracy of 5.25 cm in a two-dimensional (2-D) positioning system. And in the 3-D positioning system, the maximum positioning error is 10.27 cm, the minimum positioning error is 0.45 cm, the average positioning error is 3.97 cm, and the proportion of the positioning error exceeding 5 cm is 25 % . With a very good positioning accuracy, this system is simple and does not require synchronization processing. What is more, it can be applied to both the 2-D and 3-D localization systems, which has a broad application prospect.

Design and Implementation of Multiagent-Based Distributed Restoration System in DAS

A distribution automation system (DAS) is a power automation system to operate a power distribution network efficiently through remote control and monitoring. The most important function of the DAS is the restoration of a stable power supply to the customer when a fault occurs. Since the DAS has a centralized structure, the restoration time of the DAS takes place in about 5 min. This is too long for a customer in the digital age, so a distributed restoration system, which can shorten the restoration time from 5 min to less than 1 min is proposed in this paper. The concept of a multiagent system (MAS) for a distributed control system is applied to the proposed system to enhance its operational reliability, but there is a belief that the MAS-based distributed operations system is just a future technology. So an application method is proposed in this paper for an MAS-based distributed restoration system without significant changes to the existing DAS. The proposed system was applied to an existing DAS and tested in the Gochang Power Testing Center. The test results showed that in the most complex case, the DAS restoration time was 48 s using a code-division multiple-access module and 10 s using an Ethernet communication module.

음향 기기 및 TV 방송 수신기의 내성 시험용 기준 신호 분석

무선기기의 간헐적인 신호 또는 높고 낮은 진폭의 주기적인 신호 전송은 오디오 주파수에 간섭 신호를 발생시켜 근접 거리에 설치된 음향 기기에 잡음을 발생시킨다. 최근 이와 관련하여 Global system for Mobile Communication(GSM) 폰과 유사하게 간헐적인 신호 전송을 하는 Long Term Evolution(LTE) 폰에 의한 오디오 잡음현상이 보고되었다. 현재 국내 KN20 규격에서는 잡음에 대한 내성 능력을 확보하기 위하여 음향 및 TV 방송수신기의 내성 시험 기준 신호로 변조 주파수 1 kHz Amplitude Modulation(AM) 80 %와 Code Division Multiple Access(CDMA) 신호를 이용하고 있다. 본 논문에서는 LTE 폰의 출시에 따라 기존의 내성 기준 신호 AM과 CDMA를 GSM과 LTE 폰이 발생시키는 오디오 잡음의 수준과 비교한 후, 국내 음향 기기에 대한 내성 기준 신호의 개선을 제안한다. CDMA 신호는 음향 기기에 간섭을 거의 일으키지 않는 것으로 여겨지므로 시험 항목에서 삭제해도 무방할 것으로 판단된다. 반면, LTE는 많은 사용자가 이용하고 있으며, 음향 기기 등에 무시할 수 없는 간섭을 발생시킬 것으로 분석되므로 CDMA 신호를 대신하여 음향 기기 및 TV 방송 수신기의 내성 시험을 위한 시험 기준 신호로 규정하는 것이 바람직할 것으로 사료된다. Intermittent or periodic signals with undulating amplitudes of mobile devices cause interference noise at audible frequency to the sound system which is installed nearby. In this regard, it is recently issued that the intermittently transmissions of LTE mobile phones cause the interference noises with sound systems, similar to that of GSM mobile phones. For retaining the immunity to noises, a national regulation KN20 suggests a 1 kHz AM 80 % and a CDMA modulation signal as reference signals for immunity test of sound and television broadcast receiver. In this paper, the effects of interference noises of AM and CDMA are compared with those of GSM and LTE, and the improvement of reference signal for national immunity test of sound systems is suggested. It is recommended to delete the CDMA modulation signal from reference signals for immunity test because it hardly cause interference noise with sound systems. On the other hand, it is desirable to select the modulation signal of LTE instead of CDMA as a reference signal for immunity test of sound system and television broadcast receiver because many people use the LTE service and it is analysed that the LTE signal causes considerable interference noises.

지하수 모니터링을 위한 GeoSensor 기반의 이동식 보조관측망 프로토타입 시스템 및 사용자 인터페이스 구현

Although underground water resource has relatively less pollution rate compared with surface water, its recovery faces many difficulties due to poor management. Our country monitors underground water to manage it effectively through auxiliary observation network for underground water. In this paper, we suggest water-well auto measure system based on Geosensor for business efficiency increase of water-well management and realtime monitering. In this system is consist of user GUI(Graphic User Interface) composed with water-well information and movement sub-observation network prototype system composed with GPS(Global Positioning System) and wireless sensor node such as water temperature, water level, electrical conductivity. In this system is using the light of the sun for self-power, variety water-well information collected wireless sensor node was a wireless transmitting/receiving a using CDMA(Code Division Multiple Access) module. Also, for promote with user ease, user GUI express that water-well collected in GIS(Geographic Information System) map. For performance evaluation of the proposed system, we perform experiment using sensing information through designed sub-observation network. And we was proved superiority of the proposed system through qualitative evaluation with other paper.

Reduction of Low-Temperature Nonlinearities in Pseudomorphic AlGaAs/InGaAs HEMTs Due to Si-Related DX Centers

The linearity of conventional pseudomorphic AlGaAs/InGaAs/AlGaAs high-electron mobility transistors with planar doping in the AlGaAs layers is shown to degrade at low temperatures down to -40°C, as measured by the adjacent-channel power ratio under wideband code-division multiple-access modulation. A modified structure, in which the planar Si doping layers are placed within thin single GaAs quantum wells inside the AlGaAs barrier layers, eliminates this degradation. Deep-level transient spectroscopy and persistent photocapacitance measurements show that trapping on DX centers is effectively eliminated. The linearity improvements are therefore attributed to the elimination of this trapping. Self-consistent solutions of the Schro?dinger and Poisson equations show that the transfer of the donor electrons into the channel is essentially the same in the modified and conventional structures.

Iterative low-complexity multi-user detection for asynchronous multi-sequence signalling based bit-interleaved coded modulation code division multiple access systems

An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation (BICM) technique, a group of bits at the output of a bit-wise interleaver is mapped uniquely to a complex signalling vector belonging to an orthogonal plane sequence modulation signal space, which is constructed over a set of expanded signature sequences. This transmission system provides not only bandwidth efficiency offered by additional signal planes but also time diversity resulting from the BICM technique. It is observed that at high system traffic load error performance could degrade substantially due to user cross-correlations, multi-access asynchronism as well as channel frequency selectivity. The authors employ a 'turbo principle' receiver, consisting of a soft interference cancellation scheme, soft demappers and maximum a posteriori decoders, to avert this capacity loss by exploiting the serially concatenating structure at the transmitter. After simple mathematical manipulation, a soft space-time linear minimum mean-square error multi-user detector could even be explored on the basis of per signal plane per user. Both analytical performance-bound and computer simulation of the proposed framework in terms of bit-error rate (BER) are revealed. Further, performance comparisons with convolutionally coded and conventional bandwidth-efficient coded direct sequence code division multiple access systems under the same system conditions are illustrated. The authors have also investigated the impact of labelling maps on the BER performance.

Development of T-DMB Receiver Linking with CDMA Network for Interactive Data Broadcasting Services

In this paper, we present the configuration diagram of the interactive Terrestrial Digital Multimedia Broadcasting (T-DMB) system using the Code Division Multiple Access (CDMA) telecommunication network for the interactive broadcasting services. The system consists of a T-DMB transmission system, an interactive receiver with a CDMA module, and a return channel server. We also describe the protocol stack for providing data broadcasting service in T-DMB and propose a variety of interactive broadcasting service based on it. In order to verify the proposed service, we design and implement an interactive T-DMB receiver with a CDMA module. And also a return channel server is operated to test it, which includes the interactive contents produced in advance, responding user's request. Under the constructed test environment, the proposed service and the newly designed receiver were verified. This means that new interactive services in digital broadcasting are possible on the move by using mobility of T-DMB and CDMA.1

A $\delta$-Doped InGaP/InGaAs pHEMT With Different Doping Profiles for Device-Linearity Improvement

In this paper, delta-doped InGaP/InGaAs pseudomorphic high-electron-mobility transistors (pHEMTs) with doping-profile modifications are investigated in order to improve the device linearity. The proposed modification was based on the third-order intermodulation distortion (IM3) and the third-order intercept point (IP3) analysis using a simple equivalent circuit of the devices. The correlations of the extrinsic transconductance (Gm) with IM3 and IP3 indicate that the flatness of Gm, as a function of gate-bias causes a lower IM3 level. On the other hand, a high Gm with a flatter Gm distribution results in higher IP3 value for the device. Therefore, doping modifications that improve the flatness of the Gm distribution will also improve the device linearity. Doping modifications in the Schottky layer (Schottky layer doped) and in the channel layer (channel doped) of the conventional delta-doped InGaP/InGaAs pHEMT were investigated. It was also found that extra doping, either in the channel region or in the Schottky layer, improved the flatness of the Gm distribution under different gate-bias conditions. This achieved a lower IM3 and a higher IP3 with a small sacrifice in the peak Gm value. The power performances of these devices were tested at different drain biases. Even though it had the lowest electron mobility among the three different types of devices studied, the channel-doped device demonstrated the best overall linearity performance, the highest IP3 value, the lowest IM3 level, and the best adjacent-channel power ratio under code-division multiple-access modulation.

Performance analysis of coherence multiplexed turbo-coded optical pulse position modulated code division multiple access systems

The significant features of coherence multiplexing technique are applied to a turbo-coded optical pulse position modulated (PPM) code division multiple access (CDMA) system with differential detection, and its performance is evaluated in terms of bit-error rate (BER) by including the effects of thermal noise, beat noise, and shot noise. It is shown that around 98 users can be accommodated at a signal-to-noise ratio (SNR) of 2.0 dB for a fixed BER of 9.6688×10−6. A significant reduction in BER of around 3.2355×10−16 is achieved for an increased SNR of 7.2916 dB supporting 53 users for a source linewidth of 20 nm. On increasing the linewidth to 40 nm, the number of users is found to increase from 53 to 75 for the same BER and SNR. The reduction of BER of 3.2355×10−16, 6.6473×10−18, and 2.1089×10−19 is obtained at an SNR of 7.29 dB for increasing interleaver lengths of 10, 32, and 100, respectively. The BER reduction by decreasing the user data rates is also presented. On comparison with the direct detection, the number of simultaneous users that can be accommodated at a BER of 10−16 is found to increase from 31 to 54 users.

Fast frequency modulation optical code division multiple access communication system

An optical fast frequency modulation code division multiple access communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code named functional code is also proposed based on a shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The performance of this system is shown to be better compared with a fast frequency hopping and a spectral amplitude coding systems.

Direct Decoder of Uplink Space-Time Block Coded MC-CDMA Systems

The uplink of a space-time block coded multicarrier modulation code division multiple access (MC-CDMA) system equipped with a uniform linear array (ULA) at the base station is studied. A blind decoder that provides closed-form solutions of both transmitted symbol sequences and directions of arrival (DOAs) for all active users in one macrocell is derived without the uplink space-time vector channel estimation. The decoder uses an ESPRIT-like method to separate multiple co-channel users with different impinging DOAs. As a result, the DOAs of multiple users are obtained. In particular, a set of signal spaces, every one of which is spanned by the coded symbol sequences of an individual user, are also obtained. From these signal spaces, the original symbol sequences of multiple users are estimated by exploiting the special structure of space-time block coding (STBC) in combination with the finite alphabet property of transmitted symbols. Performance of the proposed scheme is evaluated by extensive computer simulations.

Performance of CDMA With Differential Detection in the Presence of Phase Noise and Multiuser Interference

Phase noise can be a major source of performance degradation in low-cost, low-bit-rate digital systems operating in the millimeter wavelength band. The use of code-division multiple access (CDMA) for several new applications is envisaged, and the study of the effects of phase noise shows that even CDMA systems exhibit a performance degradation comparable to that of standard modulation formats. The use of CDMA with a differential modulation at the chip level improves the system performance with a simpler demodulator at the expense of the enhancement of multiuser interference. In this paper we propose a new approach to CDMA modulation, and a possible solution is suggested to obtain a tradeoff between the performance degradation due to the phase noise and to the multiuser interference.

Bit‐error‐rate analysis for hybrid PIM–CDMA optical wireless communication systems

AbstractA hybrid pulse interval modulation–code division multiple access (PIM–CDMA) is proposed. An expression for the bit‐error rate (BER) is given. Numerical results presented are compared with hybrid PPM–CDMA and OOK–CDMA schemes. For a low number of users, PIM–CDMA achieves similar and marginally lower BER performance compared with PPM–CDMA and OOK–CDMA, respectively. For a large number of users, it offers better performance compared with OOK. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 40–44, 2001.

A GaAs/AlAs Wet Selective Etch Process for the Gate Recess of GaAs Power Metal-Semiconductor Field-Effect Transistors

A highly selective wet chemical etch process for gate recess of the GaAs power metal-semiconductor field effect transistors (MESFETs) was developed. The power MESFETs used in this study were epitaxially grown devices with a 20 Å AlAs etch-stop layer for gate recess. The selective etch process using citric acid/potassium citrate/hydrogen peroxide solution was studied. A selectivity better than 3800:1 was achieved for GaAs/AlAs layers. This selective etch was applied both to high-power, high-voltage power MESFETs and low-voltage large-periphery power MESFETs. For high-power applications, the 14.7 mm device had a breakdown voltage of 22 V. When tested at 1.88 GHz with a drain bias of 10 V, it provided a maximum output power of 38.8 dBm and a maximum power-added efficiency of 52.5%. For low-voltage applications, the 19.8 mm device was tested under IS-95 code-division multiple access (CDMA) modulation at 1.88 GHz with a drain bias of 3.5 V. Under CDMA modulation, the device showed an output power of 28.03 dBm with an adjacent channel power rejection of −29.6 dBc at 1.25 MHz offset frequency. Both devices also showed excellent uniformity in pinch-off voltages. © 2000 The Electrochemical Society. All rights reserved.

A planar gate double beryllium implanted GaAs power MESFET for low voltage digital wireless communication application

An ion-implanted planar gate power MESFET for low voltage digital wireless communication system including DCS1800 (digital cellular system at 1800 MHz) and CDMA (code division multiple access) handset applications has been developed. The process for the device developed contains double Be implantation to reduce the surface and substrate defect trapping effects. The MESFET process developed has very little gate recess (less then 200 /spl Aring/), which greatly improves the uniformity and the yield of the wafer. The 1 /spl mu/m/spl times/20 mm MESFET manufactured using this planar gate technology exhibits an output power of 32.98 dBm and power added efficiency over 53% with gain of 11.2 dB when tested at 1.9 GHz under 3.6 V drain bias voltage and 80 mA quiescent drain current. The pinch off voltage of the 20 mm devices within a wafer is -2.81 V with a standard deviation of 120 mV. The device was also tested at 3.6 V and 1.9 GHz for CDMA application. Under the IS-95 CDMA modulation at 28 dBm output power, the device gain is 10.7 dB and the device has an adjacent channel power rejection (ACPR) of -29.5 dBc at 1.25 MHz offset frequency and -44.9 dBc at 2.25 MHz offset. The test data shows that the double Be implanted devices developed using the planar gate technology have very good linearity and efficiency and can be used for the low voltage DCS1800 and CDMA handset applications.

Power PHEMT with compact device layout forlow voltage CDMA application

A high efficiency low voltage operation dual delta-doped AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) for low voltage code division multiple access (CDMA) application has been developed. When tested at 2.4 V and 1.9 GHz under IS-95 CDMA modulation, the 20.16 mm PHEMT device was found to have a linear output power of 28 dBm with a power added efficiency of 30.2%. The device also has a saturation power of 30.0 dBm with a power added efficiency of 61.5%. The high efficiency and linearity of the PHEMT at low bias voltage is attributed to the use of the dual delta-doped PHEMT structure and to the reduction of the size of the device layout. The device is suitable for low voltage CDMA applications.

Integrated-antenna push-pull power amplifiers

In this paper, the integrated-antenna concept is applied to push-pull power amplifiers (PAs). In this approach, the antenna serves as an out-of-phase power combiner and tuned load for higher harmonics. This new architecture effectively has a near-zero loss output hybrid, and results in a high-efficiency PA. The first example is a narrow-band push-pull amplifier integrated with a dual-feed patch antenna. At an operating frequency of 2.5 GHz, a maximum measured power-added efficiency (PAE) of 55% is achieved. The second example is a broadband push-pull amplifier integrated with a dual-feed slot antenna amplifier operating at 2.46 GHz which has a peak PAE of 63%, and PAE better than 55% in an 8% bandwidth. Additionally, 48% PAE is achieved with code-division multiple-access modulation and adjacent-channel power ratio better than -42 dBe at a 1.25-MHz offset.

Optimal and Suboptimal Quadriphase Sequences Derived from Maximal Length Sequences over Z _{{\bf 4}}

The paper presents families of quadriphase sequences derived from maximal length sequences over {\bf Z}_4 having good correlation properties. These are: (i) families of quadriphase sequences of period (2^r-1) from maximal length sequences over {\bf Z}_4 ; each family consisting of (2^r+1) sequences, (ii) families of quadriphase sequences of period 2(2^r-1) from interleaved maximal length sequences over {\bf Z}_4 ; each family consisting of (2^{r-1}+1) sequences. Such sequences are of interest in quadriphase modulated code division multiple access communication systems, where it is desirable to have large sets of sequences that possess low value of \theta _\max } , the maximum magnitude of the periodic crosscorrelation and out of phase auto-correlation values. The sequences over {\bf Z}_4 are viewed as trace functions of appropriately chosen unit elements of Galois extension rings of {\bf Z}_4 . Quadriphase sequences are then obtained from {\bf Z}_4 sequences, by a quadriphase mapping, \Pi , from {\bf Z}_4 to 4^th roots of unity, given by, \Pi (x) = \omega ^x ; where x \in {\bf Z}_4 and \omega = \sqrt-1 . Periodic correlation properties (correlation values and their distribution) of the quadriphase sequences are obtained by using an Abelian association scheme on the elements of the corresponding Galois extension ring of {\bf Z}_4 . The majority of the families of sequences derived are optimal with respect to the Welch lower bound on \theta _\max ; the rest being suboptimal with \theta _\max bounded by \sqrt2L , where L is the period\newpage of the sequences. However nearly half of the sequences in these families are balanced.