Doppler Division Multiple Access Research Articles

Delay Doppler Division Multiple Access Resource Allocation in Aircraft Network

Delay Doppler Division Multiple Access Resource Allocation in Aircraft Network

DDMA-MIMO Observations With the MU Radar: Validation by Measuring a Beam Broadening Effect

The phased-array radar, basically developed with the defense systems, has mainly utilized for the atmospheric radar and the wind profiling radar in the field of meteorological remote sensing, and recently it has also applied to the weather radar for research purposes. As a further development of phased-array technology, the “Multiple-Input Multiple-Output (MIMO) technique,” which has been developed in the field of communication systems, has been applied to radars. With the MIMO radar, it is possible to create a virtual antenna aperture plane beyond the actual antenna and to reduce the actual antenna size compared to that of the conventional antenna while maintaining the angular resolution. This effect is expected to reduce costs, which is one of the major hurdles in expanding phased array radars instead of parabolic antenna systems. In order to confirm the effect, an experimental observation was performed using the MU radar which is a VHF-band phased array atmospheric radar with multi-channel receivers. The MIMO technique requires orthogonal waveforms on each transmitter to identify the transmitted signals with multiple receivers, and various methods are known to realize orthogonality. In this paper, we focus on the “ Doppler Division Multiple Access (DDMA)” MIMO technique, with which slightly different frequencies are selected as transmit waveforms to separate in each receiver in the Doppler frequency domain. The observation results by measuring a beam broadening effect with the MU radar indicate that it will be a key technique for the atmospheric radar in the near future.

Mitigating Range Ambiguity Method Based on DDMA for SAR Systems

Range ambiguity can lead to deterioration of imagery quality for space-borne synthetic aperture radar (SAR). To solve this problem, we propose a mitigating range ambiguity method based on Doppler division multiple access (DDMA) in this paper. With the orthogonality of the DDMA waveform, transmit channels are separated at the receiver. Afterwards, a pre-processed operation for definition domains of different transmit channels is put forward to transform all definition domains into the same one. Thereafter, by multiplying measured data in a transmit channel by the complex conjugation of those in the other channel, a coupling phase term between the ambiguous range and the Doppler can be generated. So, utilizing the coupling phase, the echoes of different ambiguous regions can be distinguished in the slow-time domain, and they are extracted by designing time domain passband filters. Moreover, the images of different extracted ambiguous regions can be reconstructed to compose the whole unambiguous image. Finally, simulation results exhibit the effectiveness of the proposed method.

Achievable Rate Upper-Bounds of Uplink Multiuser OTFS Transmissions

In this letter, we study the achievable rates adopting two delay-Doppler (DD) domain multiples access (MA) schemes for uplink orthogonal time frequency space (OTFS) transmissions, namely delay division multiple access (DDMA) and Doppler division multiple access (DoDMA). To shed light on the system performance, we establish the achievable rate upper-bounds for both DDMA and DoDMA in comparisons to that of the conventional orthogonal frequency division multiple access (OFDMA). In particular, we show that both DDMA and DoDMA have more robust signal-to-interference-plus-noise ratio (SINR) performances against channel fluctuations compared to OFDMA and this robustness leads to higher achievable rates for both DDMA and DoDMA. To be more specific, we find that the achievable rate upper-bounds for OTFS depend only on the channel fading coefficients of different paths and the multi-user interference (MUI), while the delay and Doppler shifts also have significant impacts on that of the conventional OFDMA. Our simulation results are consistent with our derivations and demonstrate a noticeable improvement of the achievable rates for both DDMA and DoDMA over OFDMA.

Transmit Beamspace DDMA Based Automotive MIMO Radar

The time division multiple access (TDMA) technique has been applied in automotive multiple-input multiple-output (MIMO) radar. However, it suffers from the transmit energy loss, and as a result the parameter estimation performance degradation when the number of transmit elements increases. To tackle these problems, a transmit beamspace (TB) Doppler division multiple access (DDMA) approach is proposed. First, a phase modulation matrix with empty Doppler spectrum is introduced. By exploiting the empty Doppler spectrum, a test function based on sequential detection is developed to mitigate the Doppler ambiguity in DDMA waveform. Then, a discrete Fourier transform (DFT)-based TB in slow-time is formed. The proposed method can achieve waveform diversity in Doppler domain and generate a TB in slow-time that concentrates the transmitted power in a fixed spatial region to improve the transmit energy distribution for automotive MIMO radar, which is favored by medium/long range radar (MRR/LRR) applications. As compared to the conventional TDMA technique, the proposed TB DDMA approach can fully exploit the transmission capabilities of all transmit elements to ensure that the emitted power is efficiently used and inherits easy implementation.Moreover, the proposed TB DDMA method avoids the trade-off between the active time for each transmit antenna element and the frame time due to Doppler ambiguity mitigation. Simulation results verify the effectiveness of the proposed TB DDMA approach for automotive MIMO radar.

Fast-Chirp FDMA MIMO Radar System Using Range-Division Multiple-Access and Doppler-Division Multiple-Access

Frequency-division multiple-access (FDMA) in frequency-modulated continuous-wave (FMCW) radar comprises range-division multiple-access (RDMA) and Doppler-division multiple-access (DDMA). In this article, we present a method using RDMA and DDMA to realize multiple-input multiple-output (MIMO) functionality for FMCW radars. We use single-sideband modulation and quadrature phase shift keying (QPSK) modulation to implement RDMA and DDMA, respectively. These two approaches enable the simultaneous transmission of fast chirp waveforms from multiple transmitting (TX) antennas. Compared to existing works, our proposed system shows the following advantages. First, in RDMA FMCW radar, we apply overlapping binary masking to improve the unambiguous range. Second, in DDMA FMCW radar, we introduce a phase compensation method to reduce the image signals from the nonideality of QPSK symbols. Finally, we leverage these advantages of combining both RDMA and DDMA to balance the performance for FMCW MIMO radar in angular resolution, unambiguous range, and unambiguous velocity. In particular, the FMCW radar system combining RDMA and DDMA allows us to increase the numbers of TX antennas in MIMO applications. We verify our proposed radar system with measurement data on a prototype using three TX and four receiving antennas.

DDMA MIMO radar system for low, slow, and small target detection

The low, slow, and small (LSS) target detection has always been a problem for both ground-based and air-borne radar systems. The factors such as weak target reflection energy, ground clutter, and random Doppler component will have a severe impact on radar detection performance. In recent years, researches on multiple-input multiple-output (MIMO) radar system have achieved great progress. By utilising multi-channel and multi-waveform technology, MIMO radar can form equivalent phase centres and virtual apertures to provide more system freedom and enhance detection performance. To address the LSS target-detection problem, the authors propose a novel Doppler division multiple access (DDMA) MIMO radar system, which employ DDMA waveform to ensure the orthogonality of the transmit signal and avoid some of the problems in the application of frequency division multiple access (FDMA) and code division multiple access (CDMA) for the actual radar system. The sparse array is employed to supress the grating lobe of the beam pattern and improve the angle estimation performance by optimising the position of the antenna array elements. Finally, the architecture of the designed radar system is introduced and the results of the detection performance to LSS targets based on real measured data is given.

General Signal Model for Multiple-Input Multiple-Output GMTI Radar.

Multiple-input multiple-output (MIMO) ground moving target indication (GMTI) radar has been studied recently because of its excellent performance. In this paper, a general signal model is established for the MIMO GMTI radar with both fast-time and slow-time waveforms. The general signal model can be used to evaluate the performance of the MIMO GMTI radar with arbitrary waveforms such as the ideal orthogonal, code division multiple access (CDMA), frequency-division multiple access (FDMA), time division multiple access (TDMA), and Doppler division multiple access (DDMA) waveforms. We proposed a range-compensation method to eliminate the range-dependence of the FDMA waveforms. The simulation results indicate that the improved performance of FDMA waveforms is achieved utilizing the range-compensation method.

Blind velocities mitigation for MIMO GMTI radar with Doppler division multiple access waveforms

Multiple-input multiple-output (MIMO) radar with multiple transmitters and multiple receivers can achieve a larger virtual antenna array and more system degrees of freedom; thus applying it to ground moving target indication (GMTI) radar can improve the performance of GMTI. Doppler division multiple access (DDMA) waveforms are approximately orthogonal providing good minimum detectable velocity (MDV) performance. However, in such DDMA systems, a sufficient pulse repetition frequency (PRF) design freedom is required. Furthermore, these waveforms suffer from blind velocities which are serious problems, especially in radar systems with high carrier frequency or low PRF. This paper analyses the blind velocities problem and show that blind velocities are relative to variation of the PRF and/or the carrier frequency. Variable PRF techniques are widely used in conventional GMTI radar including multiple PRFs and variable pulse repetition intervals (PRI). Combined with the characteristics of the DDMA MIMO GMTI radar, this paper proposed two methods to mitigate blind velocities: “multi-PRF DDMA” which employs multiple PRFs over successive coherent processing intervals, and “PRI-dithered DDMA” which employs nonuniform sampling by dithered PRI in slow time. Simulation results demonstrate that both the methods are effective ways to mitigate blind velocities in DDMA MIMO GMTI radar systems.

MIMO Radar Waveforms and Cancellation Ratio

The performance of adaptive multiple-input multiple-output (MIMO) radar waveforms is examined. We begin by defining a metric, called cancellation ratio, for numerically screening MIMO waveforms so as to assess their clutter cancellation performance. Next, we evaluate the MISO cancellation ratio levels provided by a number of MIMO waveform classes. Finally, we describe a new MIMO waveform approach, called dithered DDMA (Doppler division multiple access), which enables high performance clutter cancellation over a large range-Doppler region without introducing ambiguous ranges or blind speeds, and without increasing the computational load on the MIMO processor.

MIMO Radar Waveform Constraints for GMTI

Ground moving-target indication (GMTI) provides both an opportunity and challenge for coherent multiple-input multiple-output (MIMO) radar. MIMO techniques can improve a radar's angle estimation and the minimum detectable velocity (MDV) for a target. However, the challenge of clutter mitigation places significant constraints on MIMO radar waveforms. In this paper, the loss of target return because of clutter mitigation (signal-to-noise ratio (SNR) loss) is the driving performance metric. The ideal, orthogonal repeated-pulse waveform is shown not to exist. Pulse-to-pulse time-varying waveforms, such as Doppler-division multiple access (DDMA), are shown to offer SNR loss performance approaching ideal MIMO systems.