Near-Field Coherent Radar Sensing Using a Massive MIMO Communication Testbed

Abstract

This paper considers the problem of radar sensing by using a large number of antennas. We use the orthogonal frequency division multiplexing (OFDM) waveform, and show that the large arrays used in massive multiple-input multipleoutput (MIMO) communications enable accurate localization in the array near-field, even at the narrow bandwidths typically encountered at low carrier frequencies. We validate our findings experimentally with a massive MIMO testbed operating at 3.5 GHz carrier frequency and 18 MHz OFDM bandwidth in an indoor environment. We consider a single moving cylinder, and demonstrate a median accuracy of (3.4, 5.6) cm in (x, y) in the near-field. We show that the accuracy is maintained with only a single subcarrier, and that the resolution increases with an order of magnitude when combining all antennas, effectively surpassing the 16.67 m bistatic range resolution set by the OFDM waveform. We use a radar symbol duration of 71.88 µs at an effective transmission period of 2.5 ms, which indicates that the radar and communication systems can be implemented in timedivision with a capacity loss of only 2.9%. Our results suggest that near-field radar sensing can be integrated into future massive MIMO systems operating at low carrier frequencies and narrow bandwidths.

Nonorthogonal waveform assisted DOA estimation for joint MIMO sensing and communication

“…However, in the considered fully nonorthogonal signal model as defined in ( 1) and ( 2), there are no exclusive subcarriers for each transmit antenna. As a result, the symbols transmitted by different antennas are mixed together in d[k, m] , such that the construction of virtual array in (8) is no longer valid.…”

“…Unlike the virtual array formed in (8), the augmented virtual array S corresponds to a single subcarrier, leading to the same propagation delay of all the virtual array antennas. Thus, the augmented virtual array S is a ULA.…”

“…With the rapid development of fifth-generation (5G) and beyond networks, the concept of joint sensing and communication has gained growing popularity due to its ability to improve spectrum efficiency while reducing hardware and energy costs [1][2][3][4][5][6]. In a joint sensing and communication system, the communication infrastructure can be multiplexed for locating noncooperative targets with a wide sensing coverage [7][8][9]. More importantly, since higher frequencies have been adopted in communication base stations [10], the finite concentrated propagation paths will be characterized by a channel in the angular domain [11].…”

Nonorthogonal waveform assisted DOA estimation for joint MIMO sensing and communication

“…In particular, we note that the virtual array formed in (7) does not correspond to a uniform linear array (ULA) since the i[z, m] is calculated with symbols on various subcarriers with different propagation delays, i.e., the first term in the Hadamard product in (7). Likewise, by substituting P in (6) Here, each column in Ṕ (:, 1 : N t ) has only one non-zero element, which means that each transmit antenna possesses an exclusive subcarrier. Hence, the formulation of virtual array is available in the same way as (7) when z = 0.…”

“…With the rapid development of fifth-generation (5G) and beyond networks, the concept of joint sensing and communication has gained growing popularity due to its ability to improve spectrum efficiency while reducing hardware and energy costs [1][2][3][4]. In a joint sensing and communication system, the communication infrastructure can be multiplexed for locating noncooperative targets with a wide sensing coverage [5][6][7]. More importantly, since higher frequencies have been adopted in communication base stations [8], the finite concentrated propagation paths will be characterized by a channel in the angular domain.…”