Buy Back Concept will not apply to preference shares. If you want redeem preference shares before maturity period, that will be known as redemption of preference shares only.
Sec 55(2) says The company redeems preference shares as per terms of issue or as varied u/s 48, it may be redeemed at a fixed time or on happening of an particular event, at any time at the option of the company or Shareholders.
So out of above content it is clear that redemption of preference shares can be done at the option of company. Hence it can redeem preference shares before it's maturity.