(22) A conventional RAKEreceiver first uses a sliding correlator to search for the multipath delay profile and a few tracking loops to acquire the channel parameters, such as the delays andthe complex gains ofthe main paths. Then it uses multiple RAKE fingers to detect data. Unlike a conventional RAKEreceiver, both path searching and tracking are done implicitly in our channel sounding subsystem because it searches and tracks all paths within one symbol period in the time domain. In a cellular system, the multipath structure may change abruptly, for example, when a vehicle turns around a street corner. The sliding correlator of a conventional RAKEreceiver suffers from the estimation delay involved in searching for the multipath delay profile. Therefore, a conventional RAKEreceiver may lose track of some newly arrived or disappeared paths, and this will degrade the system performance. At contrast, our RAKEreceiver induces much less estimation delay since our path searching and tracking are done on a symbol-by-symbol basis and it can be quickly adapted to the change ofthe channel.
III. A S IMPLIFIED I MPLEMENTATION M ETHOD FOR THE
P ROPOSED R ECEIVER A RCHITECTURE
The image rejection receiverarchitecture we described above utilizes digital signal processing techniques to enhance the IRR performance. Extra computations, such as correlation coeffi- cient calculations, are needed to implement thearchitecture. In this section, we propose a simplified implementation method for this receiverarchitecture to reduce its computation require- ments. Here, we assume the mismatching effects in the analog devices are fixed such that the computation ofthe correlation coefficients can be done in an off-line processor.
In this paper, we simulated the 2-D RAKEreceiver in both a static channel and a mobile radio channel. Our simulation results show that a threshold level should be appropriately chosen to select main signal paths and suppress interference in the channel sounder. Our simulation results show that average bit-error probability performanceofthe system is close to the theoretic result in a static channel. In the mobile radio channel, we found that the system performance degrades as the Doppler frequency increases. Onthe other hand, theperformance im- proves as AoS parameter increases as the 2-D RAKEreceiver can resolve more paths and acquire spatial diversity gain.
Moreover, the OCPN, being only a specification model for presentation of multimedia information, does not contain the communication and synchronization requirements over a net- work. Various multimedia data types have different performance requirements for network transmission and playback at the des- tination. However, the rates of communication and presentation ofan isochronous object, such as video or audio, need to be equal in order to provide continuity in playback. In order to achieve this purpose, isochronous objects can be divided into smaller units of information to be used for maintaining syn- chronization. The smallest unit is referred as a synchronization interval unit (SIU) . As an example, the synchronization in- terval for a video object can be 1/30th of a second, which corre- sponds to the playback duration of a single video frame. Hence, a video frame represents an SIU. For audio data, its SIU can be audio sample. As a result, a complete multimedia object is transmitted as a stream of SIU’s.
performanceofthespreadspectrum system requires thereceiver’s phase and frequency and its chip timing to be perfectly synchronized. The synchronization process is called code acquisition. Acquisition is basedonthe received signal’s magnitude ofthe impulse response ofthe mobile channel and sets the delay times oftheRAKE fingers. The typical RAKEreceiverarchitecture with maximal ratio combining is shown in Figure 1. The matched filter correlates the received signal with local PN code to obtain the delay profile ofthe multipath fading channel. The searcher is required to search the correlation profile. In the searcher, the threshold is set to select the peak values properly. It must set to obtain the acceptable missing probability false alarm probability.
dual-mode CORDIC, and occupies about 74k gate count.
FFT/IFFT is designed for high performance (SQNR=63 dB) and low latency (113 clock cycles) with 66k gate count. The inner receiver after FFT occupies about 69k gate count, including a CORDIC module, phase tracking circuit, and a demapping using CSI. The outer receiver operates at the same clock as the inner receiver, and therefore the Viterbi decoder requires 3 modules of ACS to achieve 54 Mbps date rate. The outer receiver with 4-b soft-decision and traceback length=90 occupies about 179k gate count. The total equivalent gate count is about 424k andthe core size is 7.3 mm 2 in 0.18-µm CMOS. The RAM-free design makes the baseband processor more convenient and process-independent in SoC design. For consideration of practical effects caused from channel and RF/analog, the integrated baseband processor written in Verilog is not only tested by test patterns, but co-simulated in the simulation environment instead.
Abstract—Direct-conversion radio architecture is a low-cost, low-power and small-size design that has been widely employed in today’s wireless devices. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that may incur severe degradation in communication performance if left uncompensated. In this paper, a new method is proposed to calibrate simultaneously a transceiver’s own transmitter andreceiver radio impairments with no dedicated analog circuit in the feedback loop. Basedon a unified time-domain approach, the proposed method is able to calibrate jointly the frequency- independent I-Q imbalance, frequency-dependent I-Q imbalance and dc offset and is applicable to any type of communication systems (single-carrier, multiple-carrier, etc.). The existing meth- ods in the literature either need a dedicated analog circuit in the feedback loop and/or are applicable only to a particular type of systems with some radio impairments present. The issue of training sequence design is also investigated to optimize the calibration performance, and analytical and simulation results show that theperformance loss due to radio impairments can be recovered by the proposed method.
Fig. 1. Multicell architecture (3, 3, 3).
So far, as previously discussed, theperformance evaluation and optimization of relay-assisted cellular networks have been limited to very specific system configurations: with a fixed number and location of RSs and/or using fixed reuse patterns. In this paper, our aim is to investigate thedownlink optimization andperformance limits of a general relay-assisted network in a multicell environment from an information-theoretic point of view. Two types of quality of end-user experience (QoE), i.e., 1) fixed-bandwidth allocation (FBA) and 2) fixed-throughput allocation (FTA), are investigated along with two path selection methods, i.e., SE basedand signal-to-interference-plus-noise ratio (SINR) based. A genetic algorithm (GA) is proposed for the joint optimization ofthe system parameters, including RS’s positions, reuse pattern, path selection, and resource allocation among different links to maximize the system SE. The theo- retical performance serves as a benchmark. For more practical relay-assisted cellular networks, the effects of modulation and coding schemes and signaling overhead that enables the RSs’
This paper includes two major contributions. 1) We introduce the term “gap-processing time” to evaluate theperformanceof different stall avoidance mechanisms. The gap-processing time is defined as the duration starting when the sequence of MAC layer data have a gap due to an NACK-to-ACK error until thereceiver recognizes that this gap cannot be recovered by the MAC layer retransmission scheme. 2) We present the closed-form expression for the gap-processing time ofthe ISA mechanism in the multiprocess SAW HARQ mechanism. The gap-processing time is related to the MAC layer scheduling policy. Currently, two scheduling policies are considered for the HSDPA system to allocate radio resource to multiple users, namely 1) scheduling-by-bundle policy and 2) interleaving scheduling policy , . The former policy schedules each user by a series of time slots, while the latter policy schedules time slots for multiple users one at a time. Therefore, with the scheduling-by-bundle policy, the gap in the reordering buffer can be detected earlier by consecutively receiving a series of packets. However, the scheduling-by-bundle policy does not ex- ploit multiuser diversity gain. Thus, the interleaving scheduling policy is adopted more commonly in current systems, since it can exploit the multiuser diversity gain , . We will focus onthe interleaving scheduling policy to derive the analytical model for the gap-processing time ofthe ISA mechanism. The relations between the gap-processing time and some system parameters in the physical layer andthe MAC layer, such as packet error rates, the number of users, andthe number of parallel processes in the HARQ mechanism, can be investigated by the developed analytical model. Since the gap-processing time affects the delay performanceand quality of service sig- nificantly, the developed analytical approach can help evaluate the overall performanceofthe HSDPA system from the higher layer user’s perspective while considering the lower physical layer impact.
A major challenge for wireless communications systems is the limited capacity due to sparse radio frequency spectrum. The capacity limit, in practice, is mainly determined by the interference rejection capability . Spread-spectrum communications techniques, realized in the form of code division multiple access (CDMA), with the advantages such as robustness against narrow-band interference with moderate power as well as noise, have been strong candidates in the next generation of high capacity wireless communications systems . In CDMA systems, signals from other users, termed as interference, can be significantly attenuated as a means of lower cross-correlation among users’
Plausible deniability is originally a term used in politics. It means the creation of loose and informal chains of commands in government, which allow controversial instructions given by high-ranking officials to be denied if these instructions become public. In the field of cryptography, deniable encryption allows an encrypted message to be decrypted to different meaningful plaintexts, depending onthe key used. This allows the sender to have plausible deniability if he is compelled to give up his encryption key. But in strictly-defined modern cryptography, it is almost impossible to design a ciphertext that can be de- crypted to several different meaningful plaintexts. In the lit- erature of steganography, plausible deniability means the ca- pability to deliver some genuine message under the cover of other innocuous messages. When the existence of hidden in- formation is detected andthe sender is forced to reveal the se- cret message, he can simply turn in one innocuous message and claim that no other information is hidden. As an example, the aforementioned real-world steganography system illustrates such a behavior. Plausible deniability has been proposed to en- hance the security of steganography systems and defend cur- rent steganalysis, as described in . In this paper, instead of diving into details of various plausibly deniable schemes, some high-level discussions about implementing plausibly deniable steganographic systems basedon generic watermarking tech- niques, andthe comparisons with the proposed system are pro- vided in Section IV-A.
The resource query, service request, and service confirmation procedures are illustrated in figure 5.
For example, if a RU wants to contact with another people called Sam, the RU has to query a RDA in advance for getting the basic information of Sam, like email address or telephone number. Further example, if the RU needs to use a color laser printer service, the RU also has to query the RDA for knowing that where is a color laser printer located at and how to access the printing service. After the RU obtains the resource basic information which includes the uniform resource indicator (URI) of that resource, the RU points and clicks the URI hyperlink to connect to the resource service form page located at the corresponding printer RSP. Then, the RU must fill out the resource service form page and submit the request to invoke the action program- a corresponding printer service CGI program. The detailed action procedures was already described in the printer RSP
4. RESULTS AND DISCUSSION
4.1. Relationship between the EEG spectrumand subject alertness
To investigate the relationship of minute-scale fluctuations in driving performance to concurrent changes in the EEG spectrum, we measured correlations between changes in the EEG power spectrumand driving performance by comput- ing the correlation coe ﬃcients between the two time series at each EEG frequency. We refer to the results as forming a correlation spectrum. For each EEG site and frequency, we then computed spectral correlations for each session sepa- rately and averaged the results across all 10 sessions from the five subjects. Figure 4a shows the results for 40 fre- quencies between 1 and 40 Hz. Note that the mean correla- tion between performanceand EEG power is predominantly positive at all EEG channels below 20 Hz. We also investi- gated the spatial distributions of these positive correlations by plotting the correlations between EEG power spectrumand driving performance, computed separately at dominant frequency bins 7, 12, 16, and 20 Hz (cf. Figure 4a) onthe scalp (Figure 4b). As the results in Figure 4a show, the cor- relation coeﬃcients plotted onthe scalp maps are predom- inantly positive. The correlations are particularly strong at central and posterior channels, which are similar to the re- sults of previous studies in the driving experiments [21, 26, 27]. The relatively high correlation coeﬃcients of EEG log power spectrum with driving performance suggest that us- ing EEG log power spectrum may be suitable for drowsi- ness (microsleep) estimation, where the subject’s cognitive state might fall into stage one ofthe nonrapid eye move- ment (NREM) sleep. To be practical for routine use during driving or in other occupations, EEG-based cognitive assess- ment systems should use as few EEG sensors as possible to reduce the preparation time for wiring drivers and compu- tational load for estimating continuously the level of alert- ness in near real time. According to the correlations shown in Figure 4b, we believe it is adequate to use the EEG signals at sites Cz and Pz to assess the alertness level of drivers con- tinuously.
Digital code tracking becomes very popular because ofthe evolution toward all digital modem implementation of DSSS systems.
In this paper, accurate nonlinear analysis for the noncoherent second-order digital code tracking loops is investigated over AWGN channels with the presence of Doppler shift. This modeling of channel finds applications in GPS  and other civilian or military satellite-based DSSS systems, where Doppler shift is due to the relative movement between the satellite andthereceiver. In the analysis, basedon a regenerative Markov chain modeling ofthe code tracking process, the lock-in range, transient response, MSE, and MTLL are evaluated more accurately than the traditional analysis. Furthermore, in a digital DLL, the adaptation of code tracking can only be done in discrete steps, i.e., quantized adaptation and that will result in significant changes in the loop performance. In this analysis, the effect of quantized adaptation is evaluated as well.