What is HR (Half-rate)?

Half Rate is a speech coding framework for GSM, created in the mid 1990s. GSM HR utilizes the Vector-Sum Excited Linear Prediction algorithm. The VSELP algorithm is an analysis-by-synthesis coding procedure. GSM Half Rate is indicated in ETSI EN 300 969. Half-rate transmission needs only half the bandwidth for information transmission, which implies that twice as many channels can be transmitted over the similar bandwidth.