The potential of time reversal in multiple antenna systems Persefoni Kyritsi, George Papanicolaou (Stanford University) Hung Tuan Nguyen, Jørgen Bach Andersen, Gert Frølund Pedersen, and Patrick Eggers (Aalborg University)

TR can achieve delay spread reduction and spatial focusing. –Delay spread* study: TR for fixed wireless applications (FWA) –Spatial focusing study: TR in a multi-user context Discussion –Normalizations and objectives –What kinds of measurements do we need? *Delay spread:

MISO TR to a single user User j TX 1 TX 2 TX N T sjsj

TR with antenna weighting: Weight selection algorithms Pure TREqual power Optimal weighting

FWA: Measurement equipment Carrier frequency: 5 GHz Transmitted power: P T = 100mW 3dB bandwidth = 25MHz 8 element uniform linear arrays (ULA) Spacing: s = /2 Vertical polarization Vertical (V) or Horizontal (H) orientation

FWA: Measument locations 29 floors (5, 19, 28) Balconies SW & NE 28 floors (19, 29) 7 floors (roof)

Classification of MISO situations Clear to cluttered Cluttered to clear

Delay spread reduction: heq / h

Spatial focusing in MISO TR to multiple users Each receiving antenna represents one of the Nr users

Interference calculation Signal on target user Interference from other users The SIR

Reminder: The near-far problem BS U1 U2

Power control scenarios The scaling factors normalize so that the total transmitted power is kept constant Additional constraints –No power control across users –Simple power control across users

Multi-user operation –N u =2 –Antennas of 2 different terminals at locations along the route separated by distance d Measurement route BS d d

Measurements f c =2.14GHz, BW > 7MHz 2 measurement routes of l=1km Transmitter –8 TX antennas –h tx =20m (Balcony on 5 th floor) Receiver _ On a trolley pulled by a van –Velocity 20-40km/hr –4 RX antennas: A1, A2, B1, B2 at the four corners

Results for N R =2, multi-user Distance in meters SIR in dB A1 A2 B1 B2 Mean Min Route Distance in meters SIR in dB A1 A2 B1 B2 Route 2 Mean Min Mean Min Route 1 Mean Min Route 2 Without power control With power control

Conclusions Spatial focusing achieved to different users with the mean SIR of up to 18dB for 8 transmitting antennas and 2 users. Multi-stream operation to a single user is not always possible