Since it's a known future event, the halving should not affect the price.
Bitcoin value is mainly psychological. I expect many people will start panic buying if they see the price start to rise near the halving which I expect it will. This can have a knock on effect too.
Mining activity, though, sees a big cut in revenue, and some miners are going to drop out. Miners presumably have run spreadsheets and know what gear goes to negative ROI after the halving, and will presumably have planned things so it more than paid for itself well before the cutoff date.
How do you know? Maybe due to the lower supply of bitcoins the price may rise?